I just finished my pond project and the last thing was the deck cover for the pump pit. The pit is 6 x 9, but I wanted the cover to also cover the drain cleanouts and autofill valve. So, the deck is 6 x 10. I contemplated for months before coming to this design. I had a custom frame made from 2.5" aluminum tubing. The tubing is 0.188 thick, fully welded at all seams. This made for a very stiff and light frame. I attached Trex decking to this frame to make the deck. To lift the deck, I installed a linear actuator capable of lifting 1000 lbs. The bottom of the actuator is supported by a clevis pivot mounted onto unistrut, all embedded in a concrete pier. I ran the control to a DPDT switch mounted high on an adjacent pergola post. Despite it's size, there is only about 1" of sag on the opposite corner from the actuator. The hinge is an 8' heavy duty aluminum piano hinge with a 5/16" pivot pin. It is through-bolted to the aluminum frame and lage screwed to double sill plates on the pit. While working in the pit, I install a fixed aluminum support at the sag end for safety (not shown in photos).
Complete pond build photos with comments at: https://photos.google.com/share/AF1Q...ZnWGN6VVBtaUp3