Does the slee belly pan support the tranny? Yes, you take the factory cross member out (yours sounds rusty). The belly pan has a beefy 1/4” uchannel welded to the skid plate that you mount the factory rear motor mount (tranny) to with the factory hardware.
It’s all one solid massive piece of steel. It uses factory bolt points plus 2 rivenuts. You bolt it on and your rock insurance policy is in effect. Nothing will help the nut behind the wheel till you learn. I’m a slow learner.
Since a lift, the full skids (aluminium coming from the front), some coaching, I have not had any underneath damage.
This all depends on what you want to drive over and still get home.
Hope that helps.