Re: Spray in bed liner for bottom paint and floor.
I used 3M bedliner spray on my little aluminum boat interior hull and there are good and bad aspects of it. The 3M is far superior than the autozone store brand, I tried the cheaper stuff and wasn't impressed.
Best thing about it is that it is much cooler with bare feet than hot aluminum on a sunny day.

It also absorbs some noise compared to the bare metal and looks nicer than the old non-skid smurf-turf factory paint.
If I had to do it all over again I would have just used gluvit as a sealer on the rivets and seams since I'm adding drop-in wood decking and the bedliner is not to be used primarily as a sealer IMO. I am considering using bedliner on the wooden decking as well, can't decide since I like to look of the wood.
I agree with the other posts regarding exterior bedliner...drag drag drag
