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lodcomm 06-24-2016 10:36 PM

Attaching Solar Panel(s) Coachmen Class B
Hello Folks,

I am getting ready to proceed with the solar panel installation on my 89 Coachem Class B. Quick Question for anyone who may have done this: What size/Length Screws did you use to actually attach the brackets to the fiberglass roof of the RV? I want to avoid punching down through the headliner :)


BBQ 06-24-2016 11:40 PM


If your roof is aluminum or fibreglass, you don't have to drill.

You can use adhesive to glue the mounting brackets to your roof.

Today's adhesives are stronger than weld !!!

You can also check out 3M VHB tape.

If your roof is rubber, then you have to use screw. Adhesive will not work.

markopolo 06-25-2016 12:04 AM

Here's a link to a VHB tape failure:

A while back I searched the web and found reports of other failures. No doubt there are success stories also. I just encourage folks to think about the potential consequences if something like a large solar panel flies off the roof & hits another vehicle or person.

BBQ 06-25-2016 01:34 AM


Originally Posted by markopolo (Post 45584)
Here's a link to a VHB tape failure:

A while back I searched the web and found reports of other failures. No doubt there are success stories also. I just encourage folks to think about the potential consequences if something like a large solar panel flies off the roof & hits another vehicle or person.


...the FAILURE was that the metal "footings" where attached to a PAINTED
surface versus fiberglass.

BBQ 06-25-2016 01:41 AM


There are 3 key factors for successful adhesives:

1. good surface prep -- the bonding area must be bondable

2. sufficient surface area for the adhesive -- you must calculate the amount of gluing surface area needed to provide sufficient bond for the required load.

3. proper mounting hardware -- you can't just glue the Z-bracket. Although I have seen people do it. But you should use proper ABS mounting hardware.

booster 06-25-2016 02:18 AM

There are very, very, many different things to worry about when using just adhesive, be it tape or liquid/caulk. The shape of the pieces being bonded have to match within the the adaptability of the adhesive, and I would consider this the concern that is most likely to bite someone. Many/most class B roofs are sloped, or even compound curved, so it is very hard on many of them to accurately determine if the foot and roof are parallel enough for tape. If you won't stick it to paint, you leave out nearly all the new units, but many of the solar folks say it is OK, so that is another choice. Of course there is factory paint and aftermarket differences also. Oxidized gelcoat, especially if it has been waxed or treated with any silicone based "reconditioner" may have worse adhesion than paint. You also need to protect the edge of the tape, if you use tape, from UV as it will deteriorate.

This is not to say adhesive won't work, as there are many documented cases where it did, but there are also documented cases where it didn't. Personal choice, and risk aversion.

For me, when I did ours on our painted, curved, fiberglass Roadtrek roof, I chose to use rivnuts (steel) and then use urethane adhesive caulk to seal and be the primary adhesive. Using the caulk allows 100% compliance with curves so much better than tape in this application. If the caulk fails, the rivnuts will keep the panel from killing anyone. I like a bit of redundancy in areas that could be hazardous in a failure. With the caulk 100% sealing all around the rivnut, and the screw into it, the chance of a leak are extremely small, and the time to do it is not bad at all, so for me there was not really any downside of consequence.

kvkite 06-25-2016 12:12 PM

Even if you use adhesives to mount, how are you going to bring the wires into the coach, without punching any holes? I think there is no way getting around it. Just punch the needed holes and use a lap sealant.

BBQ 07-22-2016 12:15 PM

The whole roof worth of solar panels (640w) held down by 6 pieces of VHB tape.

The Building of BoB the Van - Page 3 - Ram Promaster Forum

ps. not my build
not endorsing nor criticising his mounting method
just a data point

markopolo 07-22-2016 02:39 PM


Originally Posted by BBQ (Post 46323)
.................................................. ..... ps. not my build
not endorsing nor criticising his mounting method
just a data point

Good points - it's all about getting good info out there for people to read.

Two people made the effort to contact AM Solar and were advised to use screws (in addition to VHB tape): Solar panel blown away! - Page 5 - Airstream Forums

I see people recommending Dicor a lot on Class B groups. I like Dicor & use it but it's not recommended for painted surfaces as far as I know. I've used it on painted surfaces with the knowledge that it's likely not the best option.


Compatible with EPDM and TPO sheeting, it adheres firmly to aluminum, mortar, wood, vinyl, galvanized metal, fiberglass and concrete.
Stuff just seems to get repeated so often that it seems to become fact when in reality it's probably not.

It's interesting to see how cleanly the solar panel foot "pops" off in this video:

Edit: forgot to add isopropyl alcohol shouldn't have much affect according to 3M -


Testing has revealed no apparent degradation of any VHB Tape when exposed to splash testing of most common solvents, including water, petrol, white spirits, motor oil, ammonia cleaner, acetone, methyl ethyl ketone (MEK) and isopropyl alcohol.

BBQ 07-22-2016 03:12 PM

Sticking the Panel to the Roof
Sticking the Panel to the Roof using VHB tape

booster 07-22-2016 03:18 PM

I agree, everyone needs to see lots, and preferably good, information. As Marko said, lots of stuff gets repeated so much it turns into "facts" regardless of accuracy.

Interesting that AMsolar is recommending screws with the tape. When I got our first setup from them 4+ years ago, they were saying tape was enough IIRC.

That video shows some of the weaknesses of tape, in regards to failure modes. Tape tends to be very strong in a straight up pull, pretty good in pure shear (horizontal) loads, and not very good for peel strength like the force he put on the foot. If you notice that the foot held for a while and then let go almost all at once. That would indicate that the alcohol did not melt the adhesive to release it, as then it would have rocked up slowly. It is also very questionable whether or not alcohol would attack the normal solvent based adhesive used on high strength tape. If you do have a solvent that would work without wrecking the paint or fiberglass, it would slowly melt the edge of the adhesive and them creep in the tiny openings of the materials and work it's way across. I think the putty knife was the key to his getting the foot off, as it would create a stress concentrating notch along the edge of the adhesive and foam and roof. That extra stress started the peel angle which got flatter as the bracket started coming loose, accelerating the peeling and making it pop off.

The use of the solvent does bring up another point, though. If alcohol is a solvent for the adhesive, think about how much of your window washer solvent goes up the windshield and winds up on the feet. If a petroleum solvent is what attacks the adhesive, which is more likely, think about how many owners, truck washes, and detailers use "bug and tar" remover to get the tree sap off of roofs. This would be why many of the installers put Dicor or some other air curing urethane sealer around the foot base, covering the tape edge (plus UV protection which will attack the tape). The urethane sealers and caulks are very solvent resistant, very UV resistant, and when used as an adhesive be extremely strong even on larger gaps.

BBQ 07-22-2016 03:24 PM

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