DIY subfloor ballast

Just wanted to gather some thoughts.
So my brother in law (BIL) just put up his X-23 for sale. He wants a Max, we've had a few discussions about this. He mainly surfs and tubes, no ski. So I think the Max with deep hull would be ideal for him. He really likes the SFB though and was looking at Kaiyen but is dismayed by the small bow area.
I personally would choose the Max.
Since I've seen many DIY'ers here build platforms, I wanted to throw this out.
What about DIY flooring above bags? The deep hull of Max should allow this better than any other model, methinks.

I would use the same technique that aerolland used in this thread for a swim platform:
https://forum.moomba.com/showthread....f-Platform-DIY

3/4" plywood, cut, sealed and painted with Rustoleum.

The trick would be how to support the flooring above the bags. Any thoughts?
It'll be some work getting templates to close to the exact shape of the compartments, but that's prolly the hardest thing, then everything else is just cutting, sanding, staining, painting and then of course, figuring out a way to support the flooring. Would really like to hear ideas on this.

This would be a good way by BIL can get the Max and still get his SFB and storage.
For Max owners, do you feel your rear and midship compartments are deep enough for this, with the standard, 4000lb ballast factory setup? He would not be able to upgrade bags prolly, but then he could add lead instead.

I could be wrong but I looked at a 2021 Max and most of the ballast was subfloor. Only the rear bags were visible if memory serves?

Anyway, I would never use plywood (marine or otherwise) on a boat this new. No matter what you do it will eventually get water in it. Manufacturers stopped using wood 20 years ago for a reason, it just doesn't last.

HDPE (trade name StarBoard) is the correct material to use, it's available at most plastics suppliers, not cheap but not crazy either.

That would be great if that is the case. HDPE, agreed.
So would just have to cover the rear lockers. Hopefully that's true.
Found this on amazon:
https://www.amazon.com/Marine-Densit...s%2C206&sr=8-7

Not really expensive and would cover one side. Now, that HDPE is porous. Can u paint it to seal it with the rustoleum above, I wonder? I would think u could.

from what I have heard if you go down this path...make sure you got access to the bag to burp it....or have tied into the overflow...as it appears the midship bags can take a lot of air.

HDPE is waterproof and not porous, it's just textured.
No need for sealing of any kind, just cut and install.

I made an engine storage compartment in my old boat out of the HDPE. Just cut it to size to make the "box" and then i added an aluminum L shaped angle to each side and it just sat on top of the compartment dividers. Worked great. Not need to waterproof or paint.