I got lucky. I ordered a 1 gallon RotoPax for my 2200 gen fuel. I wanted it outside so I tried it up under one of the rear ‘flaps’ on my 185s. It just fit, uncannily perfect. Also, not pictured, I mounted a 2 gal diesel RotoPax of opposite wall, that I hope to NEVER use.
Gene 2001 Cummins 3/4, Lance 185s