Geoff,
I'm in the process of doing this right now. To avoid too many complications, I chose to keep the tank where it was designed which limited my choice to a custom tank, bladder, or Ronco's B192. I chose Ronco's tank. It is a bit smaller than the original, but the fit is exactly the same. The down sides are the size, limited access, and the drain fitting has to come out of the bottom. If your open to relocating the tank, it may be possible to relocate it to the V birth where the forward water tank is located. I haven't looked into this, but I'm thinking it may be possible and provide some good advantages.
Although I read a lot of good review about Ronco's customer service, I did not experience the same. It took quite a few emails and phone calls to get the order right. The person who was responding did not have a lot of technical knowledge and would not place the order without me filling out their order form. The problem was the order from has a square box you are supposed to label where you want your fittings located, but the B192 is a strange shape. I took pictures and marked them up with what I wanted and even made a CAD drawing with dimensions. In the end, they finally said I needed to talk with someone on the manufacturing floor. a few minutes later, he said it was no problem and I received shipping confirmation a day later.
When the tank arrived, the fittings were not exactly positioned where I had asked which required a small change to how I routed my vent. It isn't a huge deal, but it was frustrating. They also forgot to add the O-Ring to the inspection port. Another small annoyance is their instructions say not to use any kind of sealant on the fittings, but I could not get them to seal. I ended up using Hercules Megaloc sealant on the suggestion of a fellow member which solved the problem.
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