I don't know that most trikes rear tires would even fit into the back of a pickup bed. The clear tailgate opening width of most pickup beds is only 60".
A long bed 1/2-ton pickup, with the bed removed and a 9' long x 6-1/2' wide flatbed installed in place of the pickup bed could probably haul most trikes. At least there wouldn't be a width issue to contend with. I would probably load the trike backwards on the flatbed, so the bulk of the weight is carried behind the cab, instead of out at the rear most end of the bed.