How does the Yuba Mundo avoid having a towed bikes fork, stem,
handlebar, etc. rub or bump against the long tail framing? From the
photos it looks like there is some sort of narrow black plastic bumper
screwed horizontally to the long tail framing, but I do not see how it
alone prevents the towed bike from leaning away from the hauling bike. I
would imagine tie-downs of some sort must be needed to restrain the bike
against the long tail framing, which is why that plastic strip is
necessary as protection between the two bikes.
According to the photos, I would not think it would be too hard at all to
make a similar track-slot for an Xtracycles wide loaders. Someone
mentioned just attaching planks with cut out slots in them across the top
of the wide loaders. I do not think that would even be necessary. You
might be able to get away with just using two lengths of conduit or bars
between the front and back tubing of the wide-loaders separated by a
space, which would be the width of the tire you want to slip through.
Along the bars you would drill in adjustment holes to screw in a front
bumper for the appropriately diameter wheel(s) you intend to haul. The
rear tubing of the wide-loader would function as the back bumper of the
slot. The only major concern to this idea would be the possible need to
include some kind of padding or soft bumper system so that the tire rim
and/or spokes do not rub against the metal of the bars you use on either
side of the slot.