U.S. PATENT:Inflatable Boat-Tail with Spring Return
 

miket asked about such a thing and I happened to have one patent to share.
Ralph Potter filed for this patent when I was 4-months old.It was issued shortly before my 4th birthday.
I suspect that Ralph is long gone now,perhaps somebody will make good of his invention.58-years isn't too long to wait.

Funny this was exactly on my mind today. I searched "inflatable boattails" on google. If nobody is working on it, I might give it a real shot. I bet you could make a killing if you do it well with enough models for different cars, esp. wagons, SUV, and semis. I have an inflatable kayak made with very durable material. You pump it up in 5 minutes and it's solid, tough, light, and highly packable, and can run any whitewater and hit rocks and everything. Are you thinking about moving on this?

moving
 

I have no intention of any commercial applications.I don't have the cojones for it.

Neat (except the patent part), I wonder if you could just suck the air out and have it reliably collapse out of the way, without the spring, maybe with a bit of elastic though.