Here's the fan that I've used for the past 5 yrs and moved from vehicle to vehicle. It cost me $14 at Princess Auto (surplus) and was used to cool mainframe computers or something like that. The really nice thing about this fan is that it's rated for 12-28v DC. Hmmmm.. now what else operates within that range? If you said 'solar panels' you get a big ol' ceegar! <br> My automatic setup consists of this hooked up in parallel with the output of my solar (BEFORE the charge regulator) and it starts up automatically in the morning (slowly at first) and by noon it's pushing out a truly tremendous amount of air. Keeps my rig nice & cool (I can go to sleep with being 40 deg Celsius (104 deg F) and it turns off when the sun goes down. There's a switch hooked up to turn it off manually. It draws 1 amp and is well worth it. <br>