If you do a search on the forum you should find a bunch of good threads on different ways people mount their amps.
although it probably is not a good idea to mount your amps directly to the hull, many people, including myself, build an amp board to attach the amps to and then mount that to the hull typically by gluing it.
In my case, I used 1/2 inch birch plywood for the amp board and coated it in resin to waterproof it and then covered it in marine carpet to match the observers compartment. Then I removed strips of carpet along the hull to glue 1'X2" strips of resin coated oak to the side of the hull to give me something to screw the amp board into. For glue you can use something like liquid nails or 2 part marine epoxy. By standing off the amp board from the hull will the oak strips you can easily route and conceal the wires for a nice clean look.
Like I said, lots of good threads on here to give you some ideas