Re: Starting my Chrysler 22 Painting Project...Advice welcomed!
You wouldn't catch me under there. Why a 4x4 when a 2x10 would be considerably stronger? Or doubled 2x10's. I'd also be concerned about the ply supports at the base of your supports. I'd much rather see forward and aft movement controlled by at least a half sheet of ply running from the front support to the back support and secured with lag screws.
But...to each his own.