SOTAR recommends storing their boats partially inflated. Since it is more rigid than hypalon, I think there is some concern about the folds that will develop. I also think there is some potential for the urethane to stick together on the insides. SOTAR boats are not PVC, they are urethane coated nylon. I think many folks still store their boats rolled and they are fine, but I like to heed what the mfgr recommends. You might contact them about the heat and see which they recommend.
I am a river, babe - I've got plenty of time, I don't know where I'm going, I'm just following the lines..... - "We are water" by Shaye