I once used freezer bag plastic, a reconfigured freezer bag sealer and waxed paper like this to make 2 long tubes for sled kite spars. I blew some air in, rolled the tube around a dowel to build up air pressure, pressed a straightedge down to contain the air and sealed it up on the unpressured side. I couldn't believe that I could stand on the tube without popping it ! The rest of the kite was lighter weight garbage bag plastic. The pressure was plenty enough to keep the sled kite in shape. It flew in very light breezes.

I made another sled by overlapping plastic from a walmart bag and sealing in 2 places for each spar, leaving a long narrow tube for inflating and rolling up around the dowel. It actually took very little pressure to keep the kite in shape. When I let the reel spin free, the kite went downwind nearly horizontally and shot upward as soon as I stopped letting line out. Some type of reuseable valve could make these saleable.