I've owned at least half a dozen trucks that were rotted as badly as yours or worse,and I'm tired of welding & brazing rust repair panels in them and doing ground up restorations...the trucks will never be the same once patched up,and good luck finding someone who'll buy it later on,even if the work was done right,few folks want a patched up rotbox..you'll get less than half its resale value if your lucky...most ptach panels rust fast after being installed,and are thin gauge ,fit poorly,and aren't worth the effort and expense to install...
I would take a trip to AZ and look for a rust free tub if your frame is in excellent shape--or a whole truck,and use yours for parts...be sure the frame is good where the body mounts sat,often they look perfect till the body is off,then you find the top of the rail crumbles to dust where the mounts were...
I have "restored" way to many rusted trucks,too old for that crap now--when the 2 trucks I have rust a bit more,I'm going to ditch them and find something worth fixing up,and I'd prefer it to need an engine ,trans or driveline work--body work sucks,to be blunt,its hard work,very time consuming,and the rust always returns,usualy quickly no matter how anal you were about repairing it--and often appears somwhere "critical" like in body mount areas that didn't look "bad" when you did the sheet metal work!..
Its much easier and probably cheaper in the end to buy a rust free truck or tub....
I wasted a month patching up a rotted cab on one of my old trucks ,then saw a perfect cab in a junkyard on a truck someone scrapped that moved here from Oregon,it was mint,and I could have owned it for 400 bucks--I blew 300 just for a set of tanks and torches to weld my truck back together!..but its extremely rare to find a decent cab or tub here in New England,unless you buy one from one of those places that haul rust free vehicle back here to cut up for parts ,that get a fortune for them...