Schwalbe Fat Frank rear tire after 3000km of tarmac usage mostly, some offroad also. The brown dot is tread wear. There is no more creme coloured rubber there. To me that means, durability of those tires compares to narrow road racing tires.

I’d like to refer to an article from Vik’s big dummy blog about a long gravel road trip with mud and lots of baggage where freeloader bags got holes and other damages.
When receiving and installing my Xtracycle kit, my first impression was, that the nylon mesh and nylon loops stretched with tight tension in the V-racks did not look extremely strong and might probably wear out under heavy usage. I previously made a comment about this at the Rad-Spannerei blog (German language).
According to Vik apparently this is an issue, and I would once more recommend reinforcing the nylon material with patches of leather or whatever at least at some stressed seams and points with lot of friction. And for touring with heavy loads, better use a wide loader probably, which on the other hand might degrade handling of bicycle, especially when getting it on some train or whatever.