16 ft aluminum

Consider this stuff, a low temperature brazing product, that has better strength than hard solder, a bit like "Sil-Fos", just works with lower temperatures.

 

Ty guys for the ideas and help keep em coming. Thinking I'm going to try to make card board cut out firsts. Hard to do because it seems like a 2 person job but I'm not gonna give up.

 

Another question I have is what type of bolts and stuff to use if they are gonna be going through the aluminum.

 

Stainless, preferably 316 or 316L if much saltwater use is expected. 303 - 304 are suitable if freshwater. I agree in that the bilge stringers are the usual locations to fasten down a plywood sole. Additionally, you can screw down wooden athwart slats or cleats which can stand alone or have fore and aft slats attached. If you must use plywood, 3/8" (9mm) will do, given the distance between stringers and a relatively close and staggered 6" - 8" (150 - 200mm) fasteners spacing. Stand on the board as you drive each screw, so your weight will pin it down. Don't use spacers under the plywood, just bend it in.

 

Please don't forget to share picture with us, when you are finished.