I used boat dock foam, it's free if you find it used and it is still good once you remove the outer 2 inches of the block. I almost went with extruded polystyrene but went with expanded cause it (IMO) seems stronger and bounces back once it is compressed. It holds up the dock, so I feel it would do good in my tray.
I bought a hot knife at H freight, but a hand saw, the 3 stooges kind, not a power saw, lmao, worked great cutting my foam, but it was expanded and not extruded.
If your cutting out your tray you should widen it a little. I think mine is like 2 inches wider now and it didn't seem like much but compared to a stock tray it feels like 2 ft wider on the balance! So much nicer. I couldn't tell til I rode another ski.
Also it may be time to install a drain plug, I put mine in the pump cavity on the opposite side of the exhaust.
