I can't help with your concept, but keep in mind that most flexibles are junk. Make sure you go with a high-quality ETFE panel, such as one made by Renogy.
It will be a lot easier to make it a permanent installation since otherwise, you'll need to move the controller, too.
Good luck.
I'll be surprised to hear if the boost or regenerative braking is adjustable. That's software. You can get rid of the seat belt noise with the Carista app and their $30 OBD reader.
But no, I'm not frustrated with the braking.
One of the things that struck me with the fourth-gen was the (stock) suspension. I think they hit it out of the park. It's the best riding truck I've ever driven and I've been driving trucks for fifty years.
I've read of folks having issues, but have towed numerous times without any problems.
1. Turn the truck off and hitch up.
2. Tow
3. Turn the truck off and unhitch
4. After driving forty yards or so, it'll ask about the trailer and you select YES.
That's it.