Deep rust pocket

[wayno]

So I have some spots - mostly where my rear fenders attached to the sides where I haven't rusted clean through. I've wire wheeled them out and sprayed some rust preventer (not sure what I think of that stuff) - and then hit it with some self etching primer. Now I'm wondering if I should have just pulled out my welder and attempted to fill some of the deeper ones in (realizing I'd probably blow straight through). Just worried about bondo-ing in some of these - am I just being @n@l?