Just want to share my experience with flexible sealant on a RIB. Problem to be solved: You need to turn your RIB to cover all the surface inside the tube with the flexible sealer once you filled the tube with the liquide. The RIB's are heavy and hard to turn around.
Solution: I used a gun for rust proofing of cars(inside of doors etc.) and a compressor. I removed a valve, placed a hose with a spraying head inside the tube and spray it. The nozzle sprays the tube completely inside, The usage of the material is minimal. It worked perfectly