It won't be a "Gaspring" but it will keep the door open.
Mount a tension spring between the body and door. When the door is opened, the spring will straighten and go "coil to coil", becoming a rigid support. When you want to close the door, push in on the middle of the spring so it will fold and allow you to close the door.
All that is required is a 1/2" diameter spring about a foot long, 4 1/4-20 nuts, 4 lockwashers, 4 bolts and 2 small pieces of angle-iron. Almost any good hardware store will have the pieces.
Bob (Squidly Down Under) & Peg - 2013 Ford Focus pushing a 2011 Phoenix Cruiser 2552S
"In God we trust" to preserve our country and bring our Troops safely home.
Carry on, regardless..................