Two motorhomes ago I had a Gulfstream that also had its propane tank go bad due to rust. I also discovered that the exact Manchester tank was no longer made. I was able to find one slightly larger and had room to install it in place of the old one. I did have to modify the mounting bolts, but it wasn't too difficult. The gauge, fill, and outlet were identical to the original tank making the swap very easy.
On my last motorhome I noticed early that the onboard tank was already getting pitted and starting to rust. I cleaned it thoroughly with a wire wheel and repainted it. I touched it up annually after that. Stayed good until I traded it for my Jayco. I will service the Seneca similarly.
I'm sure many of our tanks are vulnerable to road spray, I wish Manchester applied a more durable coating initially.
2014 Seneca 37TS
Toads: 2014 Ford Explorer Sport or 2013 Ford Focus ST