I had a Co-Motion Co-Pilot (single) bike steel frame that was ordered OEM with S&S couplers and the ride was indistinguishable from a non-coupled bike. Disassemble and reassembly took some time and practice but wasn't too onerous once I got used to it. You do need a way to store and retrieve the packing case while on and after your trip.
I would recommend you buy a factory coupled frame rather than retrofitting the couplers to an existing frame. That pretty much assures the frame is made of suitable tubing and is properly aligned. The cost of the retrofit by a good, reliable frame builder followed by the repaint or powdercoat will be enough that buying a properly equipped premade frame won't be that much more. Retrofits can sometimes be dicy and I can see no advantage to a "vintage" steel frame.
The S&S web site is a goldmine of information and frame manufacturer recommendations.
Last edited by HillRider; 06-02-19 at 08:08 PM.