We have been looking at new windows for our 30ish year old house, and it certainly appears that window salesmen will give RV, car, London Bridge, etc salesmen a run for their money. Horrible knowledge, pushy, ridiculous promises, you name it.
Anyway, we have been researching and looking for a while, and have gotten very intrigued by fiberglass frame windows, which appear to be light, very strong, very durable, and have very low thermal expansion and contraction.
We just received color samples for one brand that are on a piece of the fiberglass they use for some of the window frame. This material is extremely strong.
The sample is about .08" thick 3/4" wide with a 3/16" flange down one side, and tiny flange on the other edge, maybe 5" long. It can't be bent by hand lengthwise, and it will even barely twist with large effort. It is easily stronger than vinyl, aluminum, wood, chop glass fiberglass in the same profile. Close to steel strength, I would guess.
The material is fiberglass, but made by what the call "pulltrusion".
It puts the fibers inline along the axis (they use straight fiber in the window stuff, not fabric mat), so all the strength is in a direction needed, with a full resin fill.
I think the applications into the RV industry could be pretty neat. Strong, light, non corroding or rotting- window frames, cabinet frames, running board supports, tank supports, body reinforcing for fiberglass units, etc.
When you look at the newer units built on the single wheel, front drive, Promasters, weight reduction is thing they will need to do if they want to keep adding features and options. The small Cs on Promaster could certainly use lighter/stronger parts, I would think.
I am going to be looking around to see if, and where, anyone supplies the various profiles that they make. I think it would be fun to put together a couple of test things to see how strong they are compared to the other materials. I will particularly interested to see how it would take to doing fiberglass mat/resin joint reinforcement after bolting together.