Frame Rust Specifics?

I just acquired an 86 B2000 Ext Cab. The body has no rust, including the outside and inside bed walls, but the bed floor has some holes. The guy I got it from used to leave mounds of junk in it for months at a time, holding water, and there come the holes. Looking at the top of the frame under the bed, it looks a little rusty, but I don't feel there should be any structural concerns.
The truck was bought new, and has always remained in GA, so no salt exposure.
Are there specific areas of the frame I should look close at to make sure I'm not missing anything?
I plan to simply flip this truck and sell it quick, as I have another child on the way, and my renters are flaking out, as much as I'd like to keep it.

Thanks!

Jack

right above the front leaf spring perches is the common spot I've seen.

One of the Mazdas I have is from PA so I doubt it's natural but from this one I would say in between the cab and bed on the frame and also the inner frame rails around this area.