Holding the Tank In Place
I glued some rubber strips to the hull for the tank to rest on. I also added these boards to both hold the tank away from the sides of the berth, and to act as anchor points for straps.
Leftover Foam
Helping to hold the tanks are leftover scraps of foam. Notice that I left a way to visually inspect the drain hole for leakage.
A few more foam scraps are place around the tank to help keep it from sliding around in rough seas.
Tie Down Straps
The straps pass over the top of the tank passing over rubber pads at the tank edges. The straps then pass behind another block of wood screwed into the liner. One of the screws goes through the strap. The strap is a little long as I needed some extra length to pull before tightening everything down. I left the extra length folded as shown.
The tie-down straps were purchased at a hardware store. I removed the rest of the tie-down hardware that came with them. This turned out to be the cheapest way to buy this stuff.