Dog,...I visited with all of the truck conversion manufacturers in Elkhart (and Optima in Ga) and toured their facilities.
I didn't like FRP construction (Renegade & others) use. There isn't any structure other than the plywood. Also, repairability would appear to be a nightmare if any major damage were to occure to a side panel - the whole side would need to be replaced. Then, there is always the delamination problem if water were to get into the FRP.
With Aluminum on sq tube construction, a 4' section can be replaced one at a time.
Showhauler (& others) use 1" sq tubing for walls, which doesn't leave much space for insulation and (obviously) isn't as stout as 1.5" sq tubing. As I recall, one of the manufacturers layed out the wall & ceiling structure on 24" centers instead of 16" as Hawk does. (and - Hawk puts 3" of foam under the floor). Insulation is another area that several of the manufacturers don't address very well.
Hawk also came up with 100 gallon (each) waste water tanks that fit cross ways, therefore only take up one storage bay. Our intended use is to be able to dry camp for extended periods so large water & waste water capacity was a priority.
As for workmanship, Jason Hawk is very skilled, he did the layout design with CAD, does a good bit of the complicated construction himself, and kept overall dimensional tolerances to 1/4" or less. He has a small crew & also supervises their work very closely.
If you are serious about a truck conversion, it would be most beneficial for you to spend 2 or 3 days around Elkhart "visiting" before committing to anything.
Yes, I am doing the interior myself. Hawk built the shell to my spec's, installed the propane tank, leveling jack system, generator, etc.
I have built a couple (fairly high end) bus conversions over the preceding 25 years so figured I might be able to do this without repeating previous mistakes. (of course, there are always new mistakes to be made)
I haven't posted any photos as of yet, however Hawk has several on his web page under the motorhome tab. Mine is the 43 foot all white rig with twin screw rear.
I'm still working on the interior, hope to have it finished (maybe) by next fall.
Hope this answers some of your questions