Hey Melody, thanks for the email. I’ve traveled through some extremely humid areas (Central America)… I’m taking it that your canopy does not have a headliner? That in and of itself helps a great deal. Personally I would be hesitant to put holes or van roof vents in my cap, but that may be what you want to do. I would try sleeping with a portable personal fan first and see how that helps with the condensation issue. For me it worked wonders while sleeping in those hot and humid environments. I ran mine off the inverter connected to my secondary battery.
The refrigeration setup in your van is an area where you really do get what you pay for, whether you’re paying in money or in time. The best options are the most expensive. The cheapest options are a pain and/or don’t work very well. And if you try to save money with a DIY refrigerator setup, you could end up spending a lot of time on installation.