We've used standard issue domestic regs for many years now, and have had one failure... a slow leak that was easily drained overboard
as designed. Replaced that one with another domestic unit, and no further issues were encountered. If your reg is in the self draining locker, I'd not fret about use of domestic stuff.
But I dunno about rules and regulations
from the many varied codes that one may encounter as one travels. The folks who live by ABYC standards might well disagree with my point of view, and perhaps some government
gas inspectors as well.
Keeping your regulator
dry and protected from salt
spray would always be a good idea IMO, but here in Oz lots of yachts have their LPG bottle hanging from the stern pulpit, out in the open and I don't hear many complaints about failures from the exposure.
So, there's an opinion based on personal experience and no technical expertise. Caveat emptor and all that...