I store mine in the rafters of my shop... no sun, but daytime temps are for sure over 100. I just deflate it enough so that when it heats up it doesn't build too much pressure. Storing under tarps on a trailer would seem to be the same sort of thing. With the appropriate "don't let critters naw on it" disclaimers.
Heck, I use one of my rafts without the thwarts in it for a kiddy pool for my kids.