Spinner,
I painted inside the doors with the following:
1. 2K Primer
2. 2K Paint
3. Waxguard
4. Paintable sound deadener
Waxguard is a treacle like substance used as a sealer and water repellant in new cars. Costs about $50.00 for 4 litres, and goes a long way. If you've got a later model car it's the sticky waxy honey coloured substance around all seams. I blocked off the drain holes with small sticks then painted copius quantities of the stuff around all the inner area of the door panel - it took about a month to fully dry but should keep the thing rust free for years to come. When it was dry I sprayed fish oil everywhere just in case I missed anything
Cheers,
Craig.