They look like a pretty good design, but like most things, got a good price tag, at least over here they do.
Getting parts here in Australia seams to be a tad hard, just not very many dealers and the put the price up accordingly.
Not sure if the axles will handle dual wheels, but i guess if they make the extensions they must do.
Pretty much forces me to make a lot of the stuff myself.
But dual wheels might just be the answer.