How much will the Miata and trailer weigh? I'm pretty sure MB's maximum tow rating for the 123 is 2500lbs. I'm not sure any of the hitches available for the 123's in the US are rated that high. Since there is no frame to mount the hitch, I'd be a little leary about regularly towing that much weight.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13