And since we are talking RV "decor" and not houses, the 80's extend all the way into the late 90's and even the 2000's! The mauve upholstery and tile go away, but my '99 had plenty of slate blue velvety stuff, and fairly dark wood (that went bye-bye). Never thought of your method though, I removed mine the hard way
So just in watching the beginning of your video (great idea to post that), I see a couple of things.
1) There is an "extra" gas connection that doesn't exist in the later Chinooks (including mine). That IS a flare nut you are looking at, and it does not seem to be leaking. However, there will be another one where the copper line continues on and actually attaches to the water heater (unless it's *really* different, but I've never seen a water heater come with 12" of copper line attached).
Did they add that line? Reason I ask is that on my Chinook they used long flares (which is recommended for vibration on vehicles) and those are short flares. Plus it looks like a double flare with a short male/male piece in between. BTW, where they would leak is not where the "back" of the flare and the tubing meet, but where the "front" (bigger end) of the flare meets the threads (of course check it all for good measure).
Here is an illustration of a flare fitting, for reference. You can see why they call it a flare: The end of the copper tubing is flared. (After you put the flare nut on... ahem... don't ask me how I know.) Then the next fitting has a formed cone (and threads). You slide the flare nut over a piece of tubing, flare the end of that piece, then set the "cone" of the fitting from the piece you are joining (you have to buy cone fittings, not make them), and then slide the flare nut down and screw it onto the threads (which is where you usually get any little leak, although of course it CAN leak from other places).
You can ignore the threads on the far right - they aren't flare threads and ... well, just ignore them.
Edit for this next part: I watched the end of the video and I see you did go outside and take off the grille. That would normally be the only fitting (besides the lines under the Chinook). At least on later models. So you could just check that one for leaks too. (And kind of ignore my not realizing you had already seen this when I blather on below.) BTW that large "nut" in the very center bottom that is right at the end of the video when it goes still is the drain plug/anode rod for the water heater. It does look just like a Suburban 6 gallon.
On mine (Suburban 6 gallon), you can see that final flare by taking the grille of the outside wall of the rig (in other words you are standing outside). It's right down in the forward/lower corner on mine. Let me see if I can dig up a pic. (That gas would technically leak outside, or should because that outside "pan" area should be sealed from the interior, but of course you'll still want to check it.)
Okay, I'll look for a photo.
So here is a photo of the outside "pan" area of a Suburban 6 gallon. I mis-remembered and the flare is on the forward side but midway up, not at the bottom. The whole area that you see in the photo is what you see when you are standing outside and remove the access panel on the water heater.
You can see the area where the copper comes into the exterior "pan" of the water heater through a black grommet that is also sealed (with silicone, but we'll ignore that

). On my era Chinook that copper line comes up through the floor about a foot in from the wall (by the front of the couch), then travels more-or-less horizontally over along the floor to where it goes into that hole and outside into the pan. There is no extra "vertical" copper or set of two flares inside like I see in your video (that's actually completely improper on a boat, but somewhat acceptable in an RV as long as it's secured and it's in an area you can check from time to time - vs. my buddy's other brand RV where they buried many flare fittings inside the walls in inaccessible areas - boo!) Did that second flare and extra copper just get added at the shop for some reason? Maybe you don't have a Suburban so it's different?
This is not my Chinook by the way, nor did I annotate the control buttons. But it shows the propane line and the flare fitting really well.
Okay, off to finish watching the video.
BG