My 2002 Scamp 13 came with a 45 degree A frame and a 7/8" coupler. The 45 degree frame ball couplers are no longer available and 50 degree couplers require cutting off the sides that make them less sturdy.

Since I am modifying my Scamp for off road travels with a new 22.5 degree down #10 Dexter axle and 14" wheels, I decided to install the swivel off road coupler from Cruisemaster, available in USA from U-haul, or on Ebay that would prevent trailer from decoupling at steep angles.
 

Cruisemaster™ DO35/DO45/DO65 Off-Road Couplings

Cruisemaster™ is home to innovative off-road couplings - the DO35 (3.5T), DO45 (4.5T)and DO65 (6.5T). Cruisemaster™ Couplings give you the freedom to travel Without Limits.

cruisemaster.com.au

Search for 3.5 Ton Off Road Trailer Hitch Towing Swivel Coupler
Install took about 3 hours and was very professionally done by Josh of Zabriskie Metal Fabricators in Lake Arrowhead, CA (909) 436-8205.