Ran D, you are right, solid black pipe is always best, most builders just don't take the time and use flared soft copper, which is just fine in an RV application. And of course a flexible connection for each appliance. The good quality stainless flex connectors do a good job for a safe installation and will take the vibration, no problem. The ones we always had problems with were the copper flex connectors (some are bare copper, some have a plastic coating over the copper), those suckers were notorious for cracking and leaking even in a residential application if you moved the stove around too much. We always just automatically made up a soft copper tubing connector out of the service truck to replace those copper flex connectors whenever we saw them on a service call, that's how many I have seen crack and leak. Just take about 6-8 feet of soft copper and make a big loose coil about 2' in diameter, that way you can pull the stove clear out and slide it back in without messing with the gas connection, the big coil will pull out and push back in without kinking if you coil it right. Old gasman trick, cheaper than a stainless connector, and long enough to pull the whole stove out past the cabinet to work on it without having to crawl into the greasy hole behind the stove with a couple of wrenches to disconnect the line.