Needs to be able to withstand 70 mph wind, or it will fall apart going down the highway.
Incorrect! If I am driving 70 headed into a 30 mile an hour wind, 100 mile per hour air speed. I built it out of welded steel with gussets. It'll be ok. Lots of yea and ne on the thread. What puzzles me is nobody has thrown in the "Good luck hiding that thing".