There has been past discussion on this subject and on another board, I think? The end result was anything above 10 psi should be ok. You can search this forum and a good source of Monaco info is on the Yahoo Groups Monacoers Forum. I personally have replaced my bottle (expensive) and am running 16 psi with no problems so far. The new bottle is built heavier so I think I am ok. I also can't remember why I bought that cap but I remember ordering it at the same time as the bottle. The whole mess came from Veurinlks and they are an official Monaco/HR dealer so I guess they have the specs. FWIW, they are helpful people, ask for SUE, the parts lady.
Good luck and safe travels!
Doug & Connie
2001 Holiday Rambler Imperial 41ft PBD 370hp ISL AF1 braking system
2001 Subaru Forester manual toad