Hi Kennydalglish,
I have since parted company with my IS250 but towed a Bailey Ranger 500/5 with an IS250 Sport (2.5V6 manual) for a couple of years with no problems. To be honest my only other experience of tow cars to date is our Ford Kuga but for what it is worth my feelings are that the IS Sport actually makes a very good tow car. The V6 provides plenty of pull and the suspension & tyre setup, certainly of the Sport model, gives a very firm control of the caravan. The biggest concern I had was remembering that the caravan was connected and to keep the speed within the legal limits, with the caravan balanced you will be well past the legal limits long before you notice the caravan having any real impact other than at initial pull away.
We now use the Kuga for its part time 4 wheel drive but other than pulling over grassy surfaces the IS was at least as good and in many ways a fair bit better. However, I feel that I am certainly more concious of the caravan having a bigger impact on the handling of the Kuga than it ever did the on the IS. For reference the Ford Kuga is a previous award winner as a tow car.
If you have other specific questions please post and I will try and answer but I doubt unless your caravan is a heavy one that you would have any issues. Our IS was fitted with a Witter detachable bar with twin electrics which seemed to be a VERY close match to the Lexus setup but at less than half the price.
Hope this helps,
KevM