Phat, I've got one of the support brackets like yours and made a run at using just as you did having it fit into the drain hole...problem is when I got this boat the drain sleeve wasn't right and I hollowed it out and installed one of the screw-in garboard style plugs...concerned about messing up the threads inside...I know it can be made to work, but I came up w/the support tubes above before I figured out how to do it...BTW, you mentioned PVC uses...those tubes are cut from a Minn Kota trolling motor shaft and are reinforced fiberglass...it might, but I don't think PVC would last long...
What I REELY DO LIKE in your pics are the sprinkler-heads under your boat!!...I assume you FLOOD the bottom and trailer w/one turn of a spigot...GREAT IDEA!!...
