A leak will probably run down the inside of the frame. Run your finger down on both sides. If you have to pump them ,then there is air. Look at this video. You are close. www.youtube.com/watch?v=fphcB-wB4-Q&t=109s
~ BD. "You won't find me in an old folks home" Pioneer Florida Cracker 1958 Apache Stepside 1958 Apache 1/2 ton Panel 1959 Apache 1/2 ton Panel