To break things down to basics...rust happens when iron/steel is exposed to oxygen. Rust IS ferrous oxide. To eliminate rust you must eliminate one of the two components that make up ferrous oxide...iron or oxygen. Since we want the iron, that leaves oxygen as the component to be removed. In looking at your photos it appears that the PO probably did a good job of cutting out the rot...the problem arose when the backside of the panel allowed oxygen and moisture in through the gaps in the repaired area.
Now the course of action should be to remove any remnants of the ferrous oxide (rust) and seal the area from any further incursion of oxygen/moisture. The blasting helped the outer areas but the backside of the wheel arch is now a problem to be addressed. I would remove the wheel and inspect the backside of the repaired area to see what is there. Using a wire wheel or abrasive paint stripper wheel, I would take the backside down to bare metal. If there is enough clean metal between the wheel well opening and the floor of the cab then there is a chance that you could proceed with a "chemical" fix.
Here is the way I would proceed...prepare a sheet metal patch to cover the damaged/repaired area. Scuff the panel with some coarse sand paper, ala 80 grit. Do the same for the inside of the wheel arch. Get some 3M 08115 panel adhesive and laminate the patch panel to the wheel arch. Be sure that the panel completely fills the gap between the patch panel and the body panel. Allow to set overnight. when the adhesive has cured, clean up any adhesive that has oozed out and prep the area for an application of KBS Rust Seal or equivalent...POR15, Corroseal, etc. Treat the entire backside of the wheel arch ensuring the there is a complete seal of the metal against any further moisture.
Once the backside has been repaired it is time to move on to the outer panel area. You should see that the panel adhesive has filled in the gaps/holes that were rusted through...sand these areas flush. Treat the bare metal with Rust Seal and allow to cure. Sand the treated area (don't sand through the Rust Seal!) and fill the repaired area with body filler, sand, prime, paint. Good luck...

 

A way forward has been found--I hope. As most of you have suggested, I've decided to go the metal replacement route.

My search today for an affordable solution turned up a guy who thinks he can help me. He liked the idea of using some of the metal from the fenders that were discovered in my local scrapyard. I went right out and harvested the exterior wheel arches from the old Chevy panel truck. The guy liked the condition of what I brought back and said they would be easy and not very expensive to install on my truck. He said he does wheel arch rust repair on pick-ups all the time. He charges $40 per hour for his time. If I get everything set up for him, I shouldn't have a whole lot of labor to pay for.

There are some areas of rot on my truck that were brazed that are beyond the reach of the replacement wheel arch metal from the Chevy. For these areas, I'm going to use Charlie's "chemical" fix.

I'll post some pictures next week when I get into actually making the repair. Thanks everyone for your interest and advice.

P.S. Charlie, there are no previous owners--at least not since 1958. I made (well, actually paid someone for) the repairs that were done with brazing. I just didn't realize that brazing was going to be a problem.

 

No repairs yet. I purchased a Craftsman model 50139 3 ton floor jack to gain better access to the wheel arch area. The jack, however, was defective right out of the box. After several conversations with the service department, a replacement power unit is headed my way; expected arrival--7 to 10 days!

The jack has the Craftsman name, but it's also Chinese. I should have asked forum members for recommendations. I wanted to buy American, but didn't want to spend hundreds of dollars on something I will only use occasionally. Hopefully I'll be good to go when the replacement part comes.

 

Years ago, before HF, I bought a Hein-Werner floor jack...this was in the days when only garages and service stations had such tools. Fast forward 40 years...I bought another Hein-Werner floor jack because I wanted a Made in America jack. The wording on the jack was very cryptic...something like assembled in the US from parts unknown. The jack works fine but it is very heavy and was WAY overpriced.

 

I like the size of the Craftsman. It weighs 73 pounds and is smaller than a lot of the 3 ton jacks I looked at. Some jacks I looked at were under $30 and some over $1000. I like to buy quality things, but in the case of the Craftsman, I went pretty cheap--and surprise--there's a problem.

 

I have the Craftsman (chinese) 3-ton floor jack and use it constantly. It won't hold position very long, it gradually leaks down (like an inch a day when supporting the front corner of my truck, or the transmission). At least it doesn't leak onto the floor...

 

Ross, I'm glad I'm not alone! I'm sure you use your jack more than I ever will. An inch a day drop isn't something that will bother me. A jack really only needs to hold long enough to get a jack stand safely in place. I read a lot of reviews and some people really hate their Craftsman jack, but most, like you have good things to say about it. I think all the jacks I looked at, that I could afford, had some negative reviews.

 

So, I'm still here waiting for the replacement power unit for my defective Craftsman jack. A recent conversation with the service department representative revealed that the jack supplier (not Sears) is having problems with their warehouse/shipping operation. Great. The rep I spoke with had no idea when my problem with my jack might be resolved.

As I'm waiting for a functioning floor jack, my old hand-me-down compressor decided to fail. First the tank started to leak, then the motor stopped running. I decided to avoid Craftsman for a replacement and went instead with a North Star. The unit is a 60 gal. 220v 3HP upright. Hopefully it will work. It's not American made unfortunately, but I guess it's supposed to be designed, assembled, and tested in Minnesota. It seemed to get very positive reviews. It's a little late, but does anyone have an opinion on North Star compressors?

 

There are some good Made in the US compressors out there... Saylor-Beall 5HP Air Compressor

 

See if the tank is tagged as an ASME "U" certified pressure vessel. Many states require it for tanks over a certain size, others require it for all tanks. I absolutely don't trust Chinese metallurgy and welding.

 

The North Star tank is ASME certified. Just where the tank comes from is a little sketchy. I believe North Star and Puma share components, however. The parts may come from Europe rather than Asia, but I don't really know that for sure.

 

Not a bad compressor for the $$$...the 3450 RPM motor makes these compressors quite a bit more noisy however.

 

Noisy is something I was hoping to avoid! The compressor pump turns at 950 RPM. I was thinking that was good. So what is the biggest factor for noise--the pump or the motor?

 

If you are looking for quiet compressors there are many out there now. It used to be that only the screw-type air compressors afforded any level of sound abatement but they were terribly expensive . . . very reliable, quiet but expensive. Now if you search Amazon for "silent air compressors" there are quite a few. Here is one that looks pretty good under $1K and 45 db:
https://www.amazon.com/Silent-Compre...ir+compressors

 

What you are looking for out of a compressor is SCFM...this is the volume of air produced by the pump per time period. There are many variables in how this is accomplished but for the sake of this discussion let's focus on two; volume of the cylinders and speed of rotation. If the pump has a low cubic inch displacement then it can be rotated fast enough to get a decent SCFM by speeding up the motor. Just as in an automobile engine, the faster it runs the louder it gets. Reducing the motor speed in half will reduce the noise considerably but unless the displacement of the pump is increased then the SCFM of the compressor will drop. If you look at the cylinders on compressor pumps that are designed to run with motors that turn at 3500 RPM you will see that they are noticeably smaller than those that run with motors that turn in the 1700 RPM range.