I store mine in the basement with a heavy coat of wax on them. Around August, I start measuring the temps in my sunrooom. When I see that the max temps are between 115F and 120F, I put the skis bases up in the sunroom for a day here and there. I make sure that the bases aren't in the direct sunlight (ceiling is glass) so that they don't get too hot and I make sure that they are well coated with wax so that the bases don't dry out. Although I have a hotbox, this does the same thing with no electricity costs. Plus I can only fit four pairs of skis in the hotbox.
I have friends whose attics get up to 120F who have done the same thing. Again, I do it for a day or two, I wouldn't suggest storing them in any location that gets to these temps for the entire summer.