I currently have a 1973 mobile home (aka tin box) that I am upgrading for this winter. I have done about 1/2 the windows so far (the company that made the others botched the sizes, but it's been 2 years since I bought them and they were custom at a discount) I have to fur out the openings to fit the smaller than ordered windows (they were supposed to be exact sized, but arrived made for rough opening) which I can do, but will take me longer than 1 day to do all 10. But back to the topic on hand: I'm looking at getting foam board backing that is shaped for vinyl siding (can't find the guys that have foam backed vinyl siding already made in 4'x8' sheets that I saw advertised on TV a few years back) I have my local Lowes guy (Lynnwood, WA) looking for it and it's going to be about $2,000 for it (so far) but the spec on this stuff is hard to come by. Next year I'm going to see about an insulated roof replacement. (there was one advertised that you can roll out and fasten down like a shower cap, but it's not allowed for our state) I also need to get crawlspace work done to re-do the heat ducts (partially to keep rodents out and to re-route the ducts directly to the vents as the tacked on tin to the floor joists is failing.