How many times have you walked away from a potential project because of excess rust in hard-to-repair areas? Even worse, have you ever purchased a project or finished a truck only to find hidden rot in places like rear cab corners and/or door hinge pockets? If you've yet to find yourself in such a predicament, you're either a very smart buyer, very fortunate, or a little of both! For those who have, fear not, as despite how labor-intensive this type of metal rehab can be, it's not impossible. Furthermore, with companies such as Brothers, replacement sheetmetal is but a phone call away-no donor cabs or scratch-making patch panels!
On '55-59 Chevy cabs, these two areas of disrepair are unfortunately quite common, which should help explain why aftermarket repair pieces are readily available. For a novice welder/fabricator, this job should be daunting for obvious reasons-things can get ugly quick if you don't plan each step carefully and accurately. In other words, if this is your first attempt at replacing sheetmetal-filling holes on flat surfaces doesn't count-do not use the following pictorial as your only resource if you intend to achieve professional results. By all means, take the time to consult with someone who's done it before, be it an actual professional or a friend with at least a few jobs under his belt, as it's better to have too much information collected beforehand than attempting to "learn as you go." We'll give you as much advice as we possibly can, but there's usually more than one way to skin a cat!
If you're confident this is something you can handle or are willing to give it a go, you'll need more than basic hand tools at your behest. While there are a few things you can get away with not having, you will need a good cut-off wheel (pneumatic or electric), Vise-Grips or C-clamps, an angle grinder with various grit discs, and above all else, a good MIG welder. For the best results, you should have fabricator's magnets, bodyworking hammers and dollies, Cleco fasteners, and metal shears (pneumatic, electric, or handheld). Also, it's not a bad idea to have some scrap sheetmetal (18- or 20-gauge cold rolled) just in case, you know, you come up a little short somewhere along the way.
Whether you do it yourself or have it done by a pro, replacing cab corners and hinge pockets is a lot easier in the beginning build stages than it is further down the road-so if you know it needs to be done, do it now...and do it right, so it never needs addressing again! We managed to catch and subsequently photo-document Bill Richman at Baldy's in Upland, California, tending to a Tri Five cab in desperate need of some sheetmetal attention. As noted above, this isn't a complete step-by-step story (there's simply not enough page space for door removal, alignment, and other important steps that can and often are associated with the job), so if you're working with a complete cab, you will surely need further assistance with the areas we didn't cover.
Typically, rotted-out hinge pockets aren't quite as noticeable as rusty cab corners-of course, until you open the door only to find it immediately sagging once released from the clutches of the door latch! Furthermore, rusted metal behind the hinge areas is even less detectible until you remove the front sheetmetal, as shown here. | 
Unless you're up for locating a nice donor cab (in which case, why bother replacing rusted areas?!), your only options are making repair panels from scratch or obtaining pre-made patches like these from Brothers. We highly suggest the latter. | 
Oftentimes, cab corners fall victim to what some call "gypsy bodywork," otherwise known as Bondo'd rust.... |