3 years ago we purchased a remote cabin that has an external 200 gallon
propane tank and was plumbed for some gas appliances. It turned out the
exisitng hot water tank and a small wall furnace (both gas) were failing and
I removed them. With no other gas requirements inside the cabin, I found
the feed and capped the line about 6 feet inside the cabin wall. The gas
plumbing beyond that point was old and suspiciously makeshift, so I removed
it all.

Now the place is almost fixed up, and we are considering a small gas range
and perhaps other gas appliances. I estimate there is 150 gallons of
propane in the tank, which has now been sitting for 3+ years.

Questions:

Does old propane go "bad"? When I removed some of the old piping, there
seemed to be a nasty smelling gel layer inside the pipes. Is this a
congealed version of propane? Do lines need to be reamed out before
reusing?

The regulator for the line is the last item on the feed pipe before it comes
through the cabin wall. Do these fail from lack of use?

If I replumb the gas lines, can a standard propane supplier inspect the
system or is there an offically body I need to get to inspect the new setup?
I don't want to mess with gas (or my insurance) without having someone
knowlegable who can verify my work. On the other hand, we're a fair
distance from any real city, and arranging for an inspector to get there is
problematic.

Thanks
Gary