The R31 would probably be really bad to tow with in opinion.
You've gotta remember that not only are you towing the weight of the R33 (around 1200-1300kg if I'm not mistaken), but you've also got the weight of the trailer to add to that as well.
Whilst the trailer might not look like much, most will still be around 200kg, and then you've got the physics of the whole thing, which would just make it near impossible to get a smooth ride once hitched to the R31.
Whilst the idea of a 4x4 might seem like a good one too, you've gotta remember that the majority of those around for a half decent price (around $3000 compared with the R31), are in quite bad disrepair, and may end up costing you more than it would really be worth. Especially if it's an older diesel engine.
Your best bet unfortunetly is probably a ute, or maybe even an early model Hilux van. Van's are actually fairly good for towing, as they ahve a much lower center of gravity. That and you've got a mile of space for parts, tyres and tools!