I haven't looked at how CI runs its lines or what it uses underneath. Copper tube and flare fitting are common with the 'big rig' guys, as is rubber tube for the longer runs. My best advice is to know before you start, and if you aren't sure, don't. If you do, Make absolutely sure you soap-test every single fitting. The tiniest of leaks can be a disaster. This is probably my single biggest fear now.
I had an RV fridge that dumped its ammonia, and I needed to replace the fridge _or_ have a new cooling unit installed. The cooling unit was 1/2 the price of a fridge...easy decision. The company that did the installation failed to do that soap test and missed a small leak. THey 'made it right' in the end, but it was a nearly disastrous situation.
After they replaced the fridge, I drop back to my camp site. I unplugged shore power and walked around the rig. In this process, something happened that made me need to reset a break or something, and that caused the propane spark igniter to fire. I figure the correct gas/air mixture didn't form because the rig was on the road moving --- but this leak existed while driving. Regardless, after stopping the correct combination of 'stars' aligned and 'spark' ignition system sparked, igniting not only the burner but a pool of propane that accumulated.
It burned every wire behind the fridge, which then toasted the wood. I first smelled plastic burning, then saw the billowing smoke. I ran around, turning off the propane, and grabbed an extinguisher where I distinctly remember the smell of the "wood burning" set I used as a kid as
I ripped off the exterior cover access panel, and blasted the extinguisher 'up' the wall. I was incredibly lucky. All of the 12 volt wires all destroyed, and toasted wood framing and all the fridge electronics were fried. But I was literally seconds away from burning my rig to the ground. Had this happened while I was driving....or I wasn't outside when it started...I am so fortunate. I now check my propane tank/valve for leaks just about every time I walk past my trailer now.
If you aren't sure, hire it done, and check their work. A bottle of soapy water sprayed on every joint, looking for small bubbles that 'grow' or 'percolate' indicates a leak, make a point of checking the lines every time touch the tank. If you do it yourself, double check your work then check it again. Forunately, the CI doesn't have an igniter circuit anywhere (unless you have the furnace) so your risk is less than a rig with water heaters, furnaces, fridges. But propane is full of profound amounts of energy. If that genie gets loose -- its not a good day.
I'm not trying to scare you, or tell you you can't do it --- I fix my own stuff all the time, and this is one area that is particularly 'exciting' if a mistake is made.
But the soap detection is still part of my routine.