Condensation happens when warm moist air meets a cold surface. What would happen if you bring more warm air in? More moisture, until the temperature of the surface equalizes and evaporation begins. That's sort of odd that your trunk is getting so much humid air. I get zero condensation on my amplifier which is in the trunk, nor on my carpc which is in the cabin. Perhaps there is some other reason you are getting so much humid air in the trunk that you should look into? Bad seals, and rotted pressure equalizer flap, or maybe just a hole somewhere?