Aluminized styrofoam; 2 sheets required. Home depot vinyl roll $50, oem plywood underneath (not fastened to anything), rivet holes in floor epoxied and caulked, fuel lift pump access door. Details in YouTube video below.
Click vinyl flooring
Would NOT recommend. It was a pain and has definitely shifted/popped up in spots. If we did it again we’d use a single piece of sheet vinyl.