Good job keeping the old truck alive!
Here's my $.02 on rust repairs, hope it helps.
#1 top of the importance checklist is the frame. If your frame is Swiss cheese, nothing attached to it matters.
Check your frame, paying special attention to the points at which components attach to the frame and collect water/salt; i.e. your rear cross-members, rear bumper attachment point, leaf spring perches, cab mounts, the steering gearbox, sway bars, and the transitions from boxed frame to c-channel.
Methods of stopping the rust vary depending on the severity. If it's a light surface rust, you might be ok with a thorough cleaning and wire brushing before putting your choice of rust inhibiting primer on.
For more serious rust, treat it like a tumour and cut it out. Depending on your confidence with a welder / how long the vehicle can be up on blocks for, you might have to enlist outside help. I know you are using it as a DD, so hopefully it doesn't need anything this extensive.
For more middling rust damage, where you see flaking rust scale and pitting of the metal, you need to remove all the scale, chips, anything that's not clean-as-a-baby's-butt steel. Physical removal with an air chisel, needle scaler, wire wheel grinders, etc. followed by muriatic acid, either in a bath or brushed on. Repeat until the rust is completely gone. Then, rust primer before it has a chance to flash-rust from humidity.
Something important to note with rust, it's like an iceberg; for the bit you see, there's quite a lot more you don't. If your outer rockers are toast, chances are you have to replace the inner piece too. Same with the cab corners, they have sound deadening material in there that retains moisture and rots the corner from the inside out.
Lastly, if the body panel is rusted beyond saving, you can get new pieces relatively cheaply, but with a reduction in quality. Repaired OEM is almost definitely more robust than aftermarket.
Cheers, and good luck with your project!