Wild/Weird rust

So I pulled my interior. Paneling, dash, carpet, pretty much everything. I've got zero leakage. I know it's odd from a 91 XJ, but it's the truth. However, my floor is rusting through from underneathe. And some moisture crept in under the carpet and started some rust. That's all sandable, but the rust from underneathe got through the drain plugs and now I had a few huge holes in my floor. I figured I'd sand all the rust down and spray it with some rust-stop from a can, then re-paint and re-carpet. My question is this: What the hell do I do about the bottom side? I know that just painting the top of the floor pan isn't going to stop the rust. I thought I'd sand blast everything, paint it, and then undercoat the whole car. But this seems like a lot of money for the Jeep I only paid $200 for. And about sealing up those drain plugs, how do I do that? I'm a business major, not a welder. All help and comments are much appreciated!

Hey, I'm not sure about the 91s, but in the 87s the carpets act like a sponge, they soak up water and rot the floor like you wouldn't belive. Check out my home page to see what carpets did to my 87, I don't have any leaks either. What you could do if you want to go DIY is pick up a pop-rivit gun, some sheet metal, and some rivits. Assuming you already have an electric drill, just drill, and pop. I put almost my whole floor in with pops (I probably shouldn't have, but I learned alot doing it, and it will last as long as I take care of it). If you don't want to pay to have the floor welded, pops would be the way to go, as long as you do it right (use LOTS and LOTS of rivits and good strong sheet metal) then you shouldn't do too bad.

JB weld will seal that bitch shut for good, or herculine over it like I did

Thanks guys, that keeps the inside dry, but it won't keep the underside from rusting through even more. What should I do about that?

POR-15 is amazing stuff.
http://www.por15.com/product.asp?productid=6

I POR-15'd my entire undecarriage. Rust was getting bad but no holes yet.

My 2-cent

I used a product called rust bullet for the inside,then put Dynamat down for a quite cab and that stuff seals like glue so it will keep water away from the floor as well.

http://rustbullet.com

To seal the drain the JBweld sounds good,if you sound proof with dynamat it will stick the drains to the floor as well
On the bottom side I just clean real well with the power washer and then applied truck bed liner / I thought the prep required for POR was too much
and the truck liner has held up perfectly

+3 for POR15....just did my floors inside and out....