I have a WaterSkeeter also...and I ran into the same problem ( I'm an over packer) I went to the website Oregonfishing.com and found that WaterSkeeter makes larger bags. I used a super glue of some sort the attach velcro strips to the pontoon itself, and now have way more then enough storage space on board.
Check out the website it has a bunch of stuff for tubers and Kickboats!!