OK, as promised I just took a look underneath.

  The crossover line is taken off the rear of the Extend-A-Stay that's
on the RH tank, extends back and is clamped onto the RH frame rail at
the junction of the frame crossover (jack point to jack point) bends
up and goes across, comes back down and clamps at the same point on
the opposite side, then runs up to the front of the tank where it
meets the regulator.

   I reckon that if one could manage to bung up the propane tanks and
lines, there'd probably be a whole host of other issues...

Geo/ATL
'89 Westy/ABA