I was curious about the Mountain House foods in heat, so I contacted them.

Their response:

"The trunk can get pretty hot. Although it does cool down at night, I do think that the extreme heat in a trunk will effect the
flavor. Depending on just how hot it gets where you live, the flavor profile could change in just a matter of weeks if the temps are really hot.

"I am pretty confident that after an entire summer in the trunk, there would definitely be a difference in the flavor profile. Almost like a stale flavor.

Melanie"