That is strange and not very practical in my opinion. Not only do they run below the axle, there are 2 lines.
My '74 Argosy has one line running just off of the center line of the trailer. I runs above the axle flat against the belly pan. There are tees in the line for branch lines to run to each appliance.
Do you think that maybe the guy that installed the gas lines thought that the axle tube moves like it would on a leaf spring type axle? If that were the case the lines are too close to the bottom as well. Obviously not much thought was given.
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