We tow triples (three trailers) here in OK.
In the summer its usually a truck pulling a 5th wheel trailer/ski boat with a PWC trailer bringing up the rear.
In the fall during hunting season the same truck pulling a 5th wheel trailer/horse trailer/flatbed trailer full of horse gear or ATVs.
I towed doubles commercially (two trailers) for over 11 years. Usually it one of my one ton DRW pulling a heavy GN equipment trailer with a 14'-16' cargo trailer full of tools bringing up the rear.
I pulled rv doubles.... a 5th wheel trailer with a 2500 chevy and a 3400 lb bass boat bringing up the rear (63') for eight years. Most places we stopped for the night had a drop area for extra vehicles at no charge.