If had it to do over would buy a Cheap Wire welder and flux core wire at HF or NT or even the local Farm and Home store then ship it cheap or store away after complete job.  Smaller welders, inverter welders operate far better at lower power than the commercial units we have.

'best' welds are made by the man NOT the machine or materials.

If you're real comfortable(aka skilled ) using .035 and 'autogas(75/25)' use them !  Using something new requires a learning curve.

Last truck I did  I used  Oxy/Act and  brazing rods . Built a 'cab turner' to spin it over made a HUGE difference !

if you into  a lot of repair, consider a 'southern ' cab ! I just got a box from Texas for my '97 F150...you could eat off the underside of the bed !!! Changing cabs isn't too hard IF same year. Sadly '97 is a 'one year pony'.

Ended up stitch welding the corners at the new line, Hammer as completed the work to flatten as best I could and minor amounts of filler to smooth off.

 Hey Thad,,,All great advice given and like Jay mentions it will be a sort of learning trip but certainly will give you many benefits,,,

 I recently bought one of the new Inverter arc welders that after some practice,,I wish that method had been available years ago and the whole thing only weighs about 10 Lbs and you can adjust the power from 20 amps for those body and fender panels up to 200 for the thicker stuff. The beauty of it's capabilities is they send you an adapter to use it on 120 VAC and you cut down on rod size accordingly. The primary voltage is 220 VAC and I had a chunk of wire heavy enough to make an "Extension cord" to use when on 220,,,but I'll wager ole Tim has something you can use,,, 

 The "thin stuff" does require stitch welding to keep from warping the panel, then go back and grind the gorillas down and a little Bondo and you be golden. 

 You are most welcome to use it if you want to try it out as I'm going to take it up there instead of my HEAVY Lincoln mig.

It all depends on the conditions in which you're working. Obviously in an ideal world we've all got a beautiful warm, clean and bright shop but if you're outdoors/shed has wind blowing through the flux core can be your best friend.

Really, really liking the cheap (£80) inverter unit the son bought recently. Been using that on the B project a fair bit & it's a revelation compared to my old transformer relic, laid down some of the nicest welds I've done in a good while with that thing. 

Worst thing was the learning curve of using "synergic" feed/amps on a simple dial scale when I've been used to the cheap old "10%/60% duty" power options & setting feed speed/adjusting my distance and travel to "make the best" of the two power levels for the last 20 years of odd jobs.

The inverter just seems to create a smoother arc too.  Honestly wondering where this thing has been all my life haha  Definitely worth considering if you're planning a lot of thin gauge work like truck bodies and as mentioned the smaller welders can manage some heavier stuff too, this one didn't struggle at all with 1/4" plate.

Back Flashes are evil and happened Often on the .023, as welding with hair and any disruption even to a fan blowing air will screw with that.

  That right there is the main issue I have with HF tools,,,they just do not stock any spare parts and prolly don't make em. The MGR at HF listened to my 23 minute ranting about the missing tool for my paint gun and said HF had been getting lots of complaints about spare parts for the tools they sell,,,??

 You ought to look into one of the new Inverter arc welders. It is a great all around welder and will operate on either 120 or 220 VAC and the whole thing don't weigh more that a fully loaded lunch pail,,,, I'm not sure what the max amps you could run on 120 VAC at work but figure it would do the job on the thin metal panels of TRK panels,,?

 UMMmmm,,,I started carrying some blank IOU's ,,,,and even gots a pen for you to use,,,,

  Well,,Pardner,,,since it was YOU that did introduce me to her,,,,,I be more than glad to spring for some groceries at the world Famous "Ozark Cafe",, especially their Special on Thursdays,,,!!