FLOOR: Replacing Floor... hubby and I at odds!

I dunno what effect plywood treatments have on aluminum. But I really don't think you can compare boats to campers. Plywood boats have much less aluminum to worry about, and it's much thicker. The plywood is also painted or fiberglassed, so it really doesn't touch much metal. Plus, they attach sacrificial lumps of zinc to boats to draw the corrosion, saving the more important metals like lower units and metal rudders and such.

thistle, I won't get into the forgoing debate but I will tell you my thoughts on the floor. I am rebuilding/restoring a 1961 Shasta Compact. The original floor was 3/4 standard plywood finished on one side with the bottom sprayed with an undercoating sealant. When I began the rebuild, the only places that showed rot were where water had migrated into it from the upper side, water tank, rear window, etc. So, I ended up replacing one 4 foot section (rear). Now, as I said, the whole under side was treated with a spray on undercoating and had held up well all these years. So, I did the same. When I replaced the plywood I used 3/4 ACX. I also added some additional floor joists to strengthen the rear section. Once I had the unit completed, I purchased some spray on undercoating (black stuff) and thoroughly sprayed the whole underside including the existing sections. I used a couple of coats. This method has the advantage of sealing any voids that may collect moisture as well as seal screw and nail heads. Once I got the skin on I even went around the underside and sprayed the point where the skin wrapped under. Food for thought and comment.

thistle, 3/4 ACX plywood is plywood that typically has 5 layers or plys. You may find some that have more plys but really won't hadd anything to the quality of the playwood for your purposes.  One side is considered "cabinet grade" meaning any blemishes have been filled and sanded. This is the side you would typically use to place your flooring against. The other side my have blemishes that are visible and not sanded. I would look for an ACX that is "underlayment quality". This means that the individual plys do not have voids in them. There is also another grade of plywood that uses a facing ply of several different woods like Oak, birch, etc. These would not be ones to consider for your purposes. If you talk to a reputable lumber yard and use the above information to formulate any questions you may have, they should be able to steer you in the right direction. Hope this helps and I am sure the forum will also provide you with additional help as you need it.

I would not use a metal skin for the belly. It tends to hold moisture and can cause severe floor rot. Wood breathes better, even with undercoating on it...

Thank you Vikx... I will have a good look at the other one, it seem to have held up well, but when I start renos on that one, I guess I will find out.