Looking at a '69 GMC

[682XLR8]

Good Morning all, new member here! Been lurking long enough, figured it's time to join up

I've owned a number of GM vehicles in the past so I'm already somewhat familiar with them...restored a 68 Camaro, owned an 84 GMC 1/2 ton with a TPI conversion, and currently own a 68 Vette (member of the Corvette Forum also)....latest project is my buddies 64 Impala SS (502 GM crate motor, 700R4, 9" Ford, Wilwoods all around, car is in the paint shop now, hopefully ready in time for Hot August Nights), and now I'm in the market for another truck. I have so far narrowed my choices down to 62-72, short bed, fleet or step, just depends on what I can find locally...plans for a truck would include another motor (maybe a big block ), 700R4, 2/4 drop w/ disc brakes, suspension upgrades, wheels/tires, you guys get the picture haha

Found this rig here on craigslist

https://sfbay.craigslist.org/eby/cto/6070129260.html

Truck looks good in the pics, I'm going to go look at it this weekend but my one concern is in the last pic in the ad, the rust above the door....anyone ever seen this? I'm guessing water collected on the lip just above the door and rusted through
Also, where else should I look for rust? I know that fenders behind the wheels, bottom of the doors, and cab corners can be trouble spots, what about the floors? Any other issues I should keep an eye out for?
Thanks in advance
-Randy