Metal thickness to skin the underside?

[Motor7]

The last time we were out in the Party Hut, I could feel a lot of water splashing up off the center pontoon and hitting the underside of the floor(my center toon is only 3/4'ths of the length of the boat). During my re-build I noticed that the factory made a semi lame attempt to address this issue with some thick sheet metal covering the pontoon frame openings. One of them was missing so I replaced it with some aluminium roll flashing from Home Desperate & that piece has already been mangled by the center bow wave. I now know the roll flashing is too thin.

I think I want to do a solid cover about 18' long and the full width before bending into a "U" shape is about 38". 4x8 sheets of thicker aluminium are not cheap and I would be wasting a 10" long strip off each one so the $ will add up quick and besides it will make seams that need to be lapped.

I am actually thinking about using Galvalume 24 gauge roofing which comes in 36" width and cut to my length locally. It's relatively cheap, easy to curl into the shape needed and tough. This boat will never see salt water, but am I creating a giant battery of galvanic corrosion by mating the aluminium toon structure to coated steel? If that is a bad idea, this might work if I can make it fit- 26 in. x 12 ft. Foamed Polycarbonate Corrugated Roof Panel which is .080" thick? Any other options I am missing?

[rbtnt]

.063 aluminum is pretty common to use on a pontoon. I was able to buy 10' sheets at a local recycler a few years ago for a lot less than new. The sheets had some marks on them, but no dents or bad edges. It took several phone calls to find someone that had large enough sheets. They also did one free cut per sheet which I guess is common in my area.

[Motor7]

.063 aluminum is pretty common to use on a pontoon. I was able to buy 10' sheets at a local recycler a few years ago for a lot less than new. The sheets had some marks on them, but no dents or bad edges. It took several phone calls to find someone that had large enough sheets. They also did one free cut per sheet which I guess is common in my area.

I think that is the best material, but the 'rona has driven prices up and I will need 4 sheets of the stuff. I need to shoot some video under the deck while on plane to see actually how far back the water starts to hit the xmembers.