I don't have a Mundo, but I rarely bother to lock the rear wheel on the Xtracycle. Blasted thing is hard enough to get off as it is.
I checked out a Mundo last year and you may want to factor in upgrading the components - not sure what it configurations it comes in where you are, but the shop here that carries them only has singlespeeds with a caliper brake which doesn't inspire confidence. For considerably cheaper I upgraded a secondhand MTB with a Free Radical. Not quite as stiff, but the disc brake is worth it.