I have a box truck with the translucent ceiling and there's no reason to rule out an otherwise ideal vehicle because of this. It is not an ideal material, I would much preferred to have a metal roof, however it is common enough that I wouldn't give it much weight when choosing. I wish Photobucket hadn't killed my pics, as there was multiple posts detailing how I addressed the weaknesses, but I'll hit the highlights:
1) it gets brittle and I had one hole from a branch when purchased, and I added another. I didn't want to trust it hidden under ceiling insulation and covering for my build.
2) I re-roofed the entire box prior to solar install using
Peel n Seal and
EternaBond RoofSeal around perimeter. These are both expensive (relatively) and professional quality materials...roof is now over a year old in the Florida sun and I'm pleased with the system. I've used Peel n Seal for many years at work, and the Eternabond tape is turning out to be pretty impressive.
3) Insulating between those big, deep ceiling support ribs is far easier than on about any other type of vehicle. Spray foam, a professional grade, 2-part product, is by far the best choice if you can swing the cost. A DIY kit is at least $400 in materials. I was lucky, all but two of my ceiling bays were already foamed. Spray foam not only insulates, it also greatly improves the structural value of that thin roofing.
4) I cut 3/4" Polyiso rigid foam board and used foam from a can, like max expanding Great Stuff, to lock it into place. You need to brace the panels into place while foam cures, but it works great...I have 1.5" of insulation without loosing a bit of headroom.
Hope that helps you weigh the choices...