The Nomad is built with 1mm 0.7mm 1mm butting. I don't know what butting the Club Tour uses but I would guess about 0.9mm 0.6mm 0.9mm.
Using the bike loaded offroad, I would be more concerned with wheel strength than the frame. Using the maximum tyre size would help absorb shock and make sure your spokes are well tensioned and even, particularly on the rear.
I hope this late reply is of some use.
By the way, in my experience, SJSC always reply to emails, if they receive them. I think their spam filter prevents them sometimes. It is worth trying again to another member of staff.
