Instead of using wood for the support structures, consider using fiberglass. You won't have to worry about
delamination or
rot (through the bolt holes). On a flat piece of table, cutting board, or even packing taped-cardboard, lay out 1 or 2 pieces of fiberglass (mat, cloth, 1708, etc...) in the rough shape as the vertical supports, then wet out with polyester resin. This will be the support that you glass to the hull. Once cured, cut to rough shape of the piece that you need, then glass that to the hull with epoxy and layer up 1708 to form an integrated, strong tab to support your devices/battery. The initial piece of fiberglass will be thin and is just a form for laying up additional fiberglass/epoxy to get to the thickness you want/need.
To keep the thin fiberglass piece in position, you can as
small bit of hot glue and some small pieces of mat with a hot mix of polyester resin. Once that has gone off, grind off the rough spots and tacky film, wipe with acetone, then begin laying up 1708/epoxy to bond that piece to the hull. When the supports are ground smooth and to final shape, you can then attach
cleats or whatever to hold your platform (another fiberglass sheet, epoxy/G10
cleats, or a piece of
plywood for your shelf).
If you want this semi-removable, make the tab you glass to the hull as short as possible, then bolt the removable primary support through that. When you do this, you can assemble the removable vertical support and shelf, then lower it in place onto the fiberglass tabs, then drill holes. This way, you can get your shelf to be perfectly placed so it is level and there are no low corners.
I often will assemble everything, then lower it into place on the hull and glass to the hull. This ensures that all pieces are aligned. When doing this, I don't bolt the primary supports to the hull tabs, just use C clamps. Essentially, you install in reverse: Make the shelf, make the primary support, temporarily clamp to the hull tab, then place on hull in the exact position and lightly tab with hot glue or small pieces of mat with hot mix of polyester resin. Once poly has cured, carefully remove all pieces and permanently glass the tabs to the hull. Remember to add some cardboard or whatever as a shim between the hull tab and the primary support to give space for the layers of fiberglass/epoxy you will use to secure the tab to the hull; otherwise you alignment will be off by that thickness. Use clear packing tape as a "release agent" on surfaces that will come into contact with epoxy that you don't want to glue.
The attached drawing is just a rough illustration of this modular
concept. Adjust the dimensions to fit your load.