is it neccesary to paint under carpet?

There is surface rust in three of the pans.

The worst of it is in the passenger pan, since the heater core had failed.

The driver side, and one side of the rear are not nearly as bad, but the rusty brake line was touching the floor and rotted through. I'll need to patch that.

There is also rust through in the passenger wheel house, presumably under the rear bench. (I have not pulled the rear bench yet. I have only seen it from below.) I am pulling the bench this weekend.

The underside was undercoated and seems to have held up well. There is surface rust where it has worn thin where the tires kick stuff up from the road at it, but on the inside, with the exception of catching cancer form the brake line, the rust all seems to be from above (heater core leak, spilled drinks, etc.)

I may just clean up the surface rust to bare metal where practical, clean w/Prep-n-Etch, and apply self etching primer, then spray what I can't get 100% clean with rust reformer, and go over all of it with enamel (all Rustoleum products except the Prep-n-Etch).

I might consider bedliner.

Thanks again.