I have a simple 50 watt portable solar that I toss up above the windshield, held in place with velcro (Not for traveling, just parked) It takes about 1 minute to hook up, and I have the wire running to the battery compartment. (In place perminately and neatly run) With this setup I can keep the fantastic fan running (Temp automatically comes on when inside hits about 90) and windows cracked. Fantastic Fan on low speed, uses 30 watts. I live in Murrieta, so temps here in the summer average 100.
BTW, unless it's cloudy, the house battery monitor shows 100% charged, worst case 75%