Mine lasted for 4 months with only minor deterioration. I found that on warm days though, it expanded back out and became loose fitting. I used the black poly for crawl space covering that you can get at a lumber yard. I used a heal gun to shrink it, and it required a lot of time to do so compared to using a large propane torch. Both myself a Fubeca used the same method, built a plywood aerocap the covered with heat shrink poly. The real heat shrink was quite a bit more expensive but maybe won't get loose in the heat.
If I do it again, I'm going to make my cap smooth with plywood again, but then use body filler to fill in the imperfections and paint it with an exterior grade primer and paint, I figure if the paint can stay on a house for 5-10 years, it should last a awhile on the truck.
2000 GMC AeroCap