Shopping list to build my boxes.
 

Want to make sure I don't miss anything when I go out to get the supplies to build my boxes.

3/4" Birch Plywood
1 1/2 drywall screws
Spray on glue for carpet (I already have the carpet)
Neutral Cure Silicone to seal the seams.
Wood glue (any specific recommendations)
L-brackets to screw to the mounting blocks
T-nuts
1x1 strips to brace the corners.

I'll run the wire through and seal it up and then put a powerpole connector on if I ever need to remove it.

Anything I have not taken into account from a shopping list standpoint?

Countersink bit to countersink the hole before putting the screw in.
I'd prefer liquid nail over the silicone.

Use a PVA wood glue. There is also a water resistant marine variety avalible on all your butt joins. Try to use stainless screws if possible. I've seen drywall screws rusted up in walls that don't get wet. You can also get a outdoor carpet glue that only needs to be applied to one surface not both like contact adhesive. Silicon is more plyable than liquid nails which gets brittle over time and silicon also has better water resistance. Sikaflex is much better than silicon or liquid nails but costs more, it will also bond your ali angle to the timber much better. Good luck. I also need to find time to build my sub box for my Sanger. One day soon I hope:D.

I have a countersink already so I am good there. Thank you both for the tips on glues to use. I'll take this info when I go shopping.

I'll see about stainless steel or at least weatherproof deck screws made to be in the elements.

Resin to waterproof the box.

I have resin here from other work I have done. I don't know if I am going to go to that length given where it stands. I am thinking about just going to marine grade plywood for it.

Any idea where to get Sikaflex locally?