That was years ago, no idea what the Frenchman is up to any more. Once I built mine using CCOT to a spec so close that Mr Toyota would be proud!
But I have to ask, why SS? It’s heavier, not that nice to fab with unless I guess you are TIG welding now.
I know my FJ40 upon completion will sure as s*** never have to worry about road salt and rust ever again.
Aside from limited use, the products - Cosmoline for example - will protect the metal until long after the apocalypse.
I talked to the owner at Teseven years ago, on an actual phone call, and liked what he had to say, but just couldn't part with the needed cash, especially without ever seeing one in person. Then, at some point their facility had a bad fire, and while I'm not certain of this, I believe their production of 40 tubs stopped since the fire, so as you said, I'm not sure this is a viable option today - it was more a point about the aftermarket tubs generally being slightly off from stock, since I finally go to see one first-hand.
Regarding my choice of stainless, you nailed it on your third line above - there is one primary reason - RUST. I live back east again, and have most of my life and even with good paints and prep, it is difficult to keep the rust from coming back with mild steel if a vehicle is driven in the salt bath that they apply to the roads in the winter.
Regarding weight, stainless is only marginally heavier than mild steel, so that wasn't an issue for me. Going into the build, I needed a new suspension, and planned to use Alcan. I also planned to install my 8274 Warn winch, swap out seats, etc., so I knew that I would need to provide them with real world weight - so again, adding a few pounds by using stainless wasn't a concern from my perspective.
One area were my tub is heavier is the rear sill. If you check out how I
build the rear sill, you will notice that it is likely more than twice, possibly three times the weight of stock, but this is due to its design and the only location where things got a little heavy. I also kept the large panels like the quarters in 18 gauge, while only using 16 gauge on each end of mid-tub cross member (as I call it), and several other smaller panels/patches, trying to keep the weight reletively in check. I could be wrong and since I didn't weigh the truck before I started, I can't prove this, but I doubt that the tub has gained more than 30 lbs from moving to stainless.
As far as working with stainless, maybe I'm just accustomed to it at this point, but I find it very straight-forward with MIG and/or TIG - and I used both, assuming the correct setup. With the MIG, I use 309LSi 30 gauge wire, with tri-mix gas and I'm very happy with the welding process, and the result, finding it nearly the same as MIG welding carbon/mild. Forming the stainless is a little more difficult, but again, not enough to be a problem from my perspective.
I'm also with you on Cosmoline and even Fluid Film for slightly different use cases. And although Fluid Film and similar products creap better than Cosmoline, in my view, you will likely have a difficult time getting either into lap joints with good coverage, making them less effective in these locations. One example is the lap where the top wheel well panel is spot welded to the inside of the quarter.
Also, regarding the move to stainless, if you check out my thread, you will see that I was in dire need of full panel replacement in most cases, and I figured, if I need to take the time to draw these panels in CAD, work final fitment issues, etc., there was very little downside (other than cost) to simply building the panels in stainless. And as you mentioned, the winter salt doesn't make it think twice, and next spring, it will look as it did when it was installed it, even without paint.
Coming back to cost - it can be an issue and stainless in general is roughly 40% more expensive then carbon (by memory), but I have a scrap yard near me that allows you to buy from them, and they buy companies that are going out of business and other surplusses. The 304 stainless from them was nearly 50% of retail at the time, so it all just made sense for me.