Tear it all out and start from scratch using a frame that uses a 2x3 every 12" on center from front to back, then add stiffeners glued and clamped between.
Using weights, glue and screw luwann to new floor assembly.
Lift new floor into place, set a good bead of glue along the perimeter, screw into place. Fill all gaps with tight fit foam board, lay down glue on frame members, install 3/4" plywood floor.
Should hold up solidly to future weight.
If still concerned, have metal shop fab tubular steel frame to replace wood.