My personal perference for a min wall thickness of 2 mm is that the wall will be alot more dependable under the loads of the bolts and fittings. As Grob, I too like a bit of meat (safety factor) to give security under load and abuse.

However my mainbeam is only 1.6 mm thick as all Taipan beams are and it is holding up well. There are some reports that after several years of usage small cracks may develop in these beams. 2 mm wallthickness will take care of preventing that to a large extend. So in my personal experience 1.6 mm as a min is acceptable but 2 mm is just a little more dependable.

Wouter