L.S.
If you're renting a car, rent a car seat and save yourself the worry. I've traveled with mine once. It's HEAVY and was fine (I flew SW as well and it wasn't damaged). It's just so heavy to have to lug around. The problem with the infant seat, is he may have outgrown it. If he hasn't, then take that. If it gets damaged then so what. It might also be a lot easier to carry. Don't get me wrong, I LOVE my Britax, it's just a heavy car seat to move around (which is part of the reason why it's so safe).