Getting ready to run black pipe for propane. The cabin is on piers--about 5 feet tall--and the black pipe will serve 5 appliances; there will be two branches. I have the option of running the two branch lines inside the floor joist (an enclosed floor) or on the underside of the floor (exposed). Common sense tells me to run the black pipe exposed to stubouts going up through floor so that all fittings can be monitored in the future and leaks are outside an enclosed floor cavity. I guess for those with experience, once you pressure test the system, how likely is it that black pipe will ever spring a leak? It would be a cleaner install to run inside the floor with less exposure to damage. However, what a pain to get to the pipe if it ever needed maintenance.....I would have to take the plywood off the underside of the floor).
For the same reason, I was going to run the stubouts up through the cabin floor and not in the wall cavity.....common sense tells me no fittings inside a wall where propane could pool if there ever was a leak.
Code does allow certain fittings inside enclosed spaces, just no unions, but that doesn't mean one should do it???
I wouldn't worry about the pipes being expose as long as they were not exposed to the elements from the outside. Cold weather usually will not affect them. You should install moisture traps. In essence you will be able to drain any water which will accumulate. I installed one at each stub that penetrated the floor at each appliance location. Also use hardware cloth and spray foam to sill the penetration pipes to prevent cold air and safeguard against rodents.
Black PVC tape is good also. Pressure test the system. I do not want to burst your bubble but I have seen black iron with a pin hole in the wall, before it was dry walled.