^^ 100% this
OP, it really sucks your truck was damaged, and hopefully it's fixed quickly and without excessive expense.
But honestly, that's exactly what I would expect to happen in that scenario. 300-400 miles; So that's probably five hours @ 70mph (assuming 350 miles). Let's also assume the vibration of the bungee cord is 15hz, you're looking at 270,000 agitations. Would steel (instead of aluminum) have held up better? Possibly, but that's still going to eat through your clear coat, paint, and into the bare metal. There's simply no protecting against that scenario.
Like I said, it sucks and I genuinely feel bad for that happening to a new Rap. But the load wasn't properly secured -- Hard to put any blame on the vehicle manufacturer for that.
Also, bungee cords are used to tie down patio furniture covers. Ratchet straps are for cargo. My $0.02.