Quad RL-P15 build SLLT: Is 1 1/2" MDF needed?

Hello Shack;
Is 1 1/2" MDF needed for the cabinet if I use 2" X 2" wood for bracing in a grid of 1' on all the panels and 3" thick facia for the woofers? Is this overkill??

Also what about panel bracing on the outside of the box. The box will be in an adjcent room out of view.

Thanks

Jujuman