Transmission Oil Cooling Systems for 3ltr Deisel automatic

Hi, I am looking for some advice regarding towing a caravan with our 3ltr 2WD automatic Cruising Cabin. I am considering towing a 1350kg max laden weight caravan and understand that an additional transmission oil cooling system is required. However, local automatic gearbox specialist can't find a suitable place to install one. Has any one had one fitted or do they tow without the additional cooler and if so, can the gear box and cooling system cope without? Thanks in advance.