I know that in AZ you can tow doubles if:
1) first trailer =must= be a FW; can =not= be a GN.
2) distance from front bumper to rear axle can not exceed 65', however a 10' "overhang" is allowed (rear axle to rear bumper), for an OAL of 75'.
After reading and re-reading AZ Revised Statutes, I can't find anything about licenses, truck capacity or weights.
All this being said, I've seen plenty of GNs and other utility trailers doubled to another utility trailer or implement, like a welder or mixer.
Lyle