lp lines are EXTERIOR till just before they penetrate a location.
wiring bundles are in da ROOF mostly (the tank monitor wiring is low)
unless something new has happened in assembly,
there isn't anything INSIDE frame members...
WHEN a flag box is placed where lp/brake lines cross on the under side...
the BOX bracket is notched to allow space for piping.
the post LINKED below includes photos
that show the relationship between these items...