Just wanted to update this thread. I'm going to try and drop of the existing LP lines to try and reuse them after installing the new underbelly. Plan be is black pipe and copper.
OMG!!!! Why did they use this stuff in a trailer? The black sealant around the rubber LP hoses inside the appliance bays has so strong a bond, it is actually ripping the wood underlayment apart. Yes it must be polyurethane sealant. Like those cursed power ram nails holding the underbelly to the frame, whoever spec'ed this stuff should be flogged in the public square.
I started with the trailer's fridge LP line today. Started cutting with a razor knife but ended up switching to a pair of diagonal cutters and needle nose pliers and mostly just pulling and pulling and pulling. Took about 45 minutes to get the LP line clear. I have 3 more lines to go. I know the water heater has the same goop on it, but have not opened up the furnace and stove/range but presume they have it (may not as they are interior to the trailer and don't have direct venting to the weather like the fridge and water heater do).
Needless to say I *WILL NOT* be using polyurethane sealant when I put this back in. I'm thinking a more standard caulking or even Ideal exterior duct seal putty. Yes that is wood bonded to the plug of sealant in the 2nd photo after I got it totally off the hose.
Yeah, I need to vacuum out that compartment.
Good news is I can just tie a line to the hose fitting and drop it down out of the trailer and use the line to pull it back up later. I needed to pull the LP hoses to put in a new underbelly or coroplast.
Oh, and look what I found trapped inside the LP hose at the flare fitting. Yes it was in there since this trailer was made!!!!!! Fridge worked on on LP too.