Holes and Rust

[Droff]

Looking for some advice before I take a direction on any kind of repair here. I’ve got a ’68 ¾ ton GMC and had a bad master cylinder leaking fluid into the cab, under the carpet. Once I R&R’d the MC, I decided to pull the carpet and see if there was any damage underneath.

Once I removed the sills and the carpet, I kind of moved the weatherstrip as well and found a bit of a mess. It’s not from brake fluid. The pics are the driver’s side where the weatherstrip attaches and the channel that is to the inside of it. Obviously, some water is getting in, migrating to this spot and sitting there. Both sides of the truck are this way. I should be able to see where the water is coming from a bit easier with the interior out now.

To me, it looks like my rocker panels are good, at least the outside, not sure entirely on top though, other than what I can see. There is some bubbling underneath where the door sits when closed. I don’t want to start tearing my truck apart right now, just want to get it to more of a daily driver state, which is suspension and brake work. This looks bad and I’m not so sure I want to leave it as is until I get around to doing all body repairs on the truck, but whatever I can do needs to be manageable.

I’m not a body guy but not afraid to weld and give this a shot if that’s a path to go. Can this area be cut out, cleaned up and replaced or do I need to replace a certain section – floorpan or rocker?
Thanks.