Those with welded in floors, is the back completely sealed as well? Is the false floor completely water tight? Do you have a drain plug in the false floor section to drain (condensation, relieve pressure build up due to heat in summer? Need some design ideas. Also, the 1.5" drains that I see so many have. Pros / Cons, where the hell do you get a plug that big?

1.5 ain't big that is a standard size and I think Walmart has them, I've seen some 3 inch drains!

I've always used 1" sch 80 pipe when building mine which fits a standard size plug.

Mine is welded evry couple of inches or so give or take. Just enough to let water drain and not let trash in

If it is completely sealed, put two drain plugs, one on each side at the back for exactly what you said.

Mines open in the back so water will fall into bottom of the boat to bilge out

Yea I don't mean a sealed floor that goes all the way to the transom.

that was the only problem I thought of is trash getting under it. Filling the hull with mud and crap adding weight. With a riveted floor with gutters, you could drill out the rivets everynow and then and clean out underneath it. Then just rivet it back.