I have done similar but on a larger scale. I have the Hengs Vortex fan that fits into the vent and have a small flexible solar panel taped to the roof with eternabond tape and directly wired to the fan. I have a maxair vent cover as well so during the summer the vent is open all the time while its in the storage yard.
I have this on my fifth wheel in the kitchen area which is the highest point and also installed a similar setup in the bedroom.
When daylight hits the fans kick in and suck out the heat - works for me.
