Rust under the dash

[IHaveNoIdeaWhatIAmDoing]

I recently found a rust hole under my dash right above the fuse box on the driver's side of my 83 720. Is this a common area for these trucks to rust? I can patch the hole from the inside but I am worried about not being able to stop the rust, because I can't access the rust area from the outside. It is blocked by the frame section behind the fender. When it rains it drips into the passenger compartment from the water draining out of the cowling. I will get some pictures of the area tomorrow. I am hoping some of you guys have had experience with rust in this spot and have some tips on how to best repair it.

[bottomwatcher]

I have the leak. Never had much success stopping it for long. If you seal it from the inside and pour a little epoxy down the cowl it might buy you a year of no leaks. At some point I am going to remove the fender and cut a window into the body to get to the cowl.

Edited May 10, 2023 by bottomwatcher
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[IHaveNoIdeaWhatIAmDoing]

Here are some photos of the spot.

[IHaveNoIdeaWhatIAmDoing]

11 hours ago, bottomwatcher said:

I have the leak. Never had much success stopping it for long. If you seal it from the inside and pour a little epoxy down the cowl it might buy you a year of no leaks. At some point I am going to remove the fender and cut a window into the body to get to the cowl.

Yeah I have a couple ideas to patch the hole I am just worried about it continuing to rust away and get worse.