Looks like you're about ready to slap some power on there and go bust some waves.
I was wondering how your tank was going to fit into the scheme of things. Yeah that filler hose doesn't like to bend so I see your concern but if it doesn't bend without putting downward pressure on the tank against the top then you might be able to use a 90 degree molded piece of filler hose and use a metal coupler to the main hose.
The front casting deck looks really large in the pic, it should be very roomy up there. My mind has been going thinking about how to design mine so that's an interesting design you have going with 2 large side compartments and a forward hatch too is what it looks like. I was thinking I would need to set my consoles in and use them for the rear deck support as I think you did with yours. Are you using different sizes of angle AL and what thickness are you finding is best?