As an FYI my wife and i did just what you are pondering in converting a cargo van to a nice camper van. There is a build thread _at the Sportsmobile forum here
_. You were also asking if there is such a forum that people have done what you are asking...well the SMB forum is such a place. Look in the "Homebuild" (_LINK
We purchased ours new in October 2010 looking like this...
And today it is fully loaded/functional for our needs as this:
My wife and i did all the insulation and major interior work in about two months working on our two days off each week. Then in the spring of 2013 we had a custom van shop do some interior mods. BUT she and i did have everything working as we'd designed (sleep/cook/shower/potty) and used the rig for two seasons before the interior face lift...so... this can be done. AND we get OOOHHHs and AAHHHs nearly everywhere we go. This van is also my wife's daily driver.
IF i were to do it from scratch in the current market i would strongly look at the new Dodge Ram Promaster van. It would make a nice platform. Since it is just you, you could start out very simply with utilizing an electric space heater (you said you'd be in park settings?) and something like a NuWave cooktop
(we use one for all our _burner_ type cooking in our full time rig). Also you could utilize something simple like the Separett Weekender
toilet system (no plumbing needed). Think out of the box simple and you could have some fun. On the bed? Spend the few bucks on a Froli-Sleep System
...the BEST out there!!
OH, as for being allowed in parks, our rig(s) get comments as i said every place we park
...and visitors. Also, in the place that we full time (an RV & Golf Resort on the Oregon Coast, arguably the nicest park in the area) they have a written "10 years or newer" policy...yet i've seen 20 year old Blue Birds and even older converted school "Hippie" buses
Best wishes on your ponderings and project,