would help to cut some access holes into the body cavity, especially above the wheel tubs, but where it'd be really useful would be below floor level front and back of the wheel wheel - see
that pic, where the junk builds up is the low points below the curve of the wheel arch .... if you open that area enough you should be able to clean it out well and slop in a good coat of epoxy or something [Zero Rust for me] and make some functional drains for any condensation to escape, warm air only holds moisture temporarily, as soon as it cools down it condenses on the cold metal again
I figured a plan for the doors like that too, cutting open the largest depressed area on the front face of the door to access inside well to paint, then make a screw on cover so it can be accessed anytime in the future
Bill