This is the combo that I plan to do on my 122 and would recommend to anyone in the same situation.

Strip the floors down to BARE METAl on the inside. Apply POR-15 (www.ipduas.com) to the whole thing. You will only need 1 coat. This is a moisture-hardened polyurethane so it will NEVER allow moisture through it again. It also will neutralize small amounts of surface rust. This will ensure that you wil never have to redo the floors again, as would be the case with zero-rust or any other conventional coating. Additionally, the stuff needs no primer and is a relatively clean application (no spray mess.) Just make sure you use a disposable brush and latex gloves. It doesnt come off of skin.

On the underside, a couple of coats of sprayable undercoating from any auto supply store should do the trick well.

For sound dampening, Dynamat works wonders if you have the money, but personally I think the product is ridiculously expensive. For economy's sake, buy a roll of torchdown asphalt roofing. You can get this at any home supply store and it will form to your floorpans with a bit of heat from a propane or butane torch. This is asphalt based, like dynamat, is almost as good at soundproofing, and is really inexpensive. I have plenty of hotrod pals who do this on a regular basis.

Over top of that, you can put a felt matting layer. This adds more sound dampening and a soft cushy feel to your floor. You can get this at any upholstery shop for minimal cost.

And of course, cover this in your rubber mat and you will have a rustproof floor that you will never have to worry about again, even if your vehicle leaks.

Good luck,
Josh Hartung