Not a 100 percent sure on the heat issue, but I can tell you they are pretty near indestructible
mods. I've dropped mine, kicked mine, scratched and scuffed it up, knocked it off a tractor onto the
shop floor, covered it in grease, left it in the car overnight and throughout the day... And the list goes on. I have not had a single problem yet. I don't think heat will be an issue as long as your o-rings are fitted properly, especially in the bottle cap. The worst that'll happen is your bottle might get a little softer and easier to squeeze, I have noticed that happens when it gets hot out while I'm working or when I leave it on hot engine parts.
I remember seeing one post where somebody dropped their Reo off a Harley at a good speed and it still works...
Basically just give the Reo a shot, you won't be disappointed!