Hi you asked about insulation........Fiber glass simply "holds" heat better than Foam could ever dream of. Visualize the soft featherd down of birds. That down "holds" the heat close to their body. Fiberglass is "loft" alot like down, in the sense that it holds/retains heat. Like I said eleswhere..........I tried many other alternitives besides fiberglass............with failure. I am a carpenter, foundation to finish. Its my trade. I just use what works. About those really long screws? Consider another approach. How about furring out the wall to a specific distance, say 2". If you MUST attach to those plates, do so only at the bottom, middle and top. Place your wooden furring strips over the plates, anchored to them. Space them along the walls, vertically, say every 16" on center. You can insulate the wall space behind. This way, you can choose any length screw you want, because you are just screwing to those furring strips. You will wera a lot of drill-bits out drilling through that steel, and it isn't necessary. Cutting off the tips of the screws with a grinder is not anefficent use of your time or talent. Next, about those jerry cans.................have you cosidered [just one option, and the easiest] buy one of those cool cerramic vessels that you fill with a pretty blue 5 gal. plastic bottle..........like a cooler fountain......you know, with the push-spigot. I have one of them, and they are easily obtained at a lot of health food stores. Or, and more exspensive, [and I set my bus up this way, as well as another........] install a pressurized water system. It takes a bit of money, but you can have pressurized showers, water pressure at your facuet............if you are interested, I can tell you where to obtain everything you will need............and how to do it. As for the grey water...........[some work involved here, but I set up another bus with this system] create a sturdy frame beneath the floor of the Uhall [somewhere in the metal framing of the vehical, there is always a place for the placement of a 25 gal water tank; or a 50 gal. water tank......or a series of such tanks. One of them can hold your fresh water [the pressurized system] and the other tank your grey water. They use this approach in the fancy RVs. Greywater is not toxic; and dumping it just anywhere is risky, if you are noticed by some "Good Sam" type person. So, don't be noticed. Let me know if any of this is useful to you.