I use my 1980 300TD (non Turbo) to tow a 6' (length) x 4 ' (width) x 1'6" height box trailer when I go camping (and being summer here, I have just come up from two weeks down the coast - between 25 to 35°C every day).
I always balance the load on the trailer so I can lift the draw bar by hand, but I reckon it would be 1.5 tones across the axles, fully laden.
I recently added a frame to the top of the trailer and put a canvass covering - The resultant box now measures 6' x 4' x 4' height from the bottom of the trailer (or 6' off the ground). Whilst great for packing (cause you just neatly place every thing inside), pulling this brick (behind a bigger brick of a car) has a fair amount of drag on the engine (bad, bad aerodynamics). So much so, that going up hills (of which, fortunately, there are very few here) on the freeway can reduce me down to 60km\h and on go the hazard flashers. Before, when I just covered the trailer load with a canvass, speed up hill was relatively unaffected.
I haven't added a trans cooler and not thought I would need one.
