Need advice on floor supports

[Newtgadget]

Need advice on proper floor supports above both tanks please.
We are in process of draining both fuel tanks and replacing hoses. Prior to buttoning things back up, we want to ensure we are doing things correctly. Please see photo below of what was existing.

We found 3/4 plywood underlayment only covering the front tank. The rear tank had no subfloor above it, only the deck. Should this not be one continuos piece of plywood covering both tanks and be sealed in case deck leaks thru a bit?

Do you have any other suggestions for subfloor support or is this commonplace?

I was thinking a continuos perimeter made out of aluminum or stainless "L" we could bend in my shop as well as crossmember made of asme.

Do I have to worry about galvanic corrosion if we got his route or am I over thinking this and just redo it in wood?

Thanks for your replies in advance!

 

[Newtgadget]

After speaking to the fuel tank manufacturer, they advised highly against any type of pressure treated wood in the vicinity of the aluminum fuel tanks. Their experience is that pressure treated wood when wet, leaches some sort of chemical which is attacking the aluminum. They advise to utilize plain fir which has been sealed, fiberglass, aluminum or stainless only.

Below is what we have started. Hopefully will get it finished over the weekend.

We had leftover 16 gauge stainless from one of our jobs.......so if its free.....its for me!

 

[family affair]

On another boat we learned the hard way that pressure treated lumber, water, and aluminum are a very bad combination. If I hadn't seen the damage with my own eyes, I wouldn't have believed it!