Karel you are a brave man! Mogs are generally formidable off road, and have equally formidable fuel consumption. I recently went and watched a Europa Truck Trial event where they were climbing things I wouldn't attempt without a rope! They got over the high C of G problem by filling the tyres with water...hmm! The portal axle design means that if you drop a wheel into a hole, or it digs in it will do so deeply; you'll need another Mog to get it out. The floor of any box you put on the back will be at least 1.5 m off the ground, add to that the 2 m box height and it starts to feel ponderous and evilly tall. Take one for a couple of hours test drive, with a box on the back. They're very slow and noisy. Then reconsider just how much SERIOUS off-roading you're going to do in your adventures.
A guy called John Speed wrote a really comprehensive book on the preparation of an overland 'van. He had a Mog expedition vehicle but preferred a Merc 4x4 panel van about 6 m long, I've seen it, it's lovely. check out http://www.020.co.uk/travelvans/ it's pricey but worth it. I also found http://www.unimog.org.uk/ while looking for the ideal base for a 4x4 camper van. I had the luck of finding a fully overland equipped Iveco Daily 4x4 (even a generator on board) which, although it's no dune buggy, is surprisingly capable off road (diff locks et al). It is also very well behaved on long hauls and returned less than 15l/100km over the last 20000km in Maroc and Europe.
For the stuff dreams are made of look at http://www.actionmobil.at/english/e_index2.html and go weak at the knees. My conclusion on the ideal base vehicle with low C of G and manoeuvrability etc. it's either the Supacat HMT (http://www.supacat.com) or even more fun the Gaz Vodnik (http://www.vodnik.com/index_en.htm) ; barges and ferries, broken bridges and water holes no longer a problem
Oh well it costs nothing to dream.
Happy trails
Luke