Jim,
What a great idea. You've got me thinking now. I was about to fabricate a deflector for the back of my truck topper but a solar module would accomplish both the deflection and be charging on the road. I'm going to check some wind specifications re the deflection and wind speed but even if my design ideas mean it can't be done, mounting a panel flat for travel is still a great idea.
How much A/C run time are you able to do now, since you have the system configured? *(for those not up to Jim's installations, he is using a small 5K BTU A/C unit run by inverter and the 12V system)*
Do you have the size of that 450W panel stored in memory? I can look it up, too, just getting lazy, lol.