This is nothing more than brainstorming...
I do not have tilting panels so I do not actually know what will work well. For a cheap, DIY idea, I thought perhaps a door hinge with one side bolted to the panel frame and the other side bolted to the angle bracket on the roof might work. Two of these on each long side (of the panel) might allow a guy to remove the door hinge pins on one side to tilt one way or vice-versa. Maybe something with a locking pin/bolt on the short sides of the panel and some way to lock the door hinge pins to really secure when traveling.
Again... thinking about loud.
Edit: Apologies - I have very large 60 volt panels... smaller panels may not require anything nearly as heavy as a door hinge.