Since there is not a lot of room on the hot tub deck, the bench will be perched on the edge of the deck, tilting back. Attach 4x4 support posts to the edge of the deck.
Lay pressure-treated 2x4s across the seat supports and screw into place. After the 2x4s are attached to the seat of the bench, begin securing 2x4s to the back of the bench with coated deck screws. Be sure to leave a small gap between each beam to give the bench a more uniform look.