Home built heating element

We are working on a project to send to go pros 100,000 ft up in the sky. unfortunatly at that height temperatures are horrible. so I am hoping to create a heating element to control temperature internally. I am not an electronics guy but i am at a technical school there is not a short supply of guys who know what their doing in that department. if anybody could help that would be alot of help. heres some specs that i have.

- 2 day battery life
- 70*F ± 5*F constant
- realitively small like 5" x 5" x 5"
Thanks

A lot depends on the size of the box and its insulation. If it is well insulated (and maybe black) it should be pretty easy. Maybe a foam box with a clear window for the camera? Two days is a long time for a heater. Do you have a plan for a battery?

Howdy, I'd be tempted to go chemo-thermal: a slow exothermic reaction inside an insulation box And outside another insulation box. I'd gather a representative temp curve from some weather people then talk to some chemical engineers about reaction rates & civil engineers about insulation characteristics of temperature gradients & heat transfer.

Between the two, you should be able to get a good guess on what'll work. Next step is to stage the temps to be encountered (serious refrigeration) & try some combinations with an RF temp gauge and see what Really is workable. Good Hunting... <<<)))