Ah, got it. Didn't think about CNG. Makes sense, but still hard to believe Hunter didn’t consider a propane locker.
But if not, then an external tank may be the only option.
On my O’Day 322, a PO wanted to use larger tanks, so they modified the propane locker by extending the depth quite a bit. I don’t like it because the dang thing is so deep. But my point is that if you have small lockers in the cockpit, you might be able to create a propane locker by drilling a hole in the bottom, glassing in a drain barb, running a drain line to a new above the waterline thruhull. A chore for sure, but if you have a locker without a drain, it could be done.
But you can’t use a large lazarette for this. Unless you put a small tank locker in the lazzarette and did the drain line like above. There are some commercially available propane lockers available for this application or an “on the rail’ mount.
Greg