Storm cellar trap door

[trim4u2nv]

Rebuilding a 1844 porch with a trap door (flat) we would like to counterweight.  Has anyone else done this to make opening easier.  Size is 36 x 96 inches 2x6 framing topped with 3/4 inch pressure treated plywood and 5/4 x 6 PT deck boards.  Have already put on 3 web hinges on the narrow end rated 500 lb each.  We have 24 inches from the hinge to a stone wall to hang weights.  Current ideas are to use a steel cantilever arm and cable suspended disc (barbell) weights.  Have seen many jobs with gas shocks like you see mounted on a hatchback vehicle, but they seem to fail at the worst time.

 

http://youtu.be/zcYxSXz82EQ