Hi,
I have recently part ex'ed a manual 2001 2.9 petrol Volvo S80 for a 2001 GS300. Like yourself I tow a caravan with a max weight of 1485kg. I talk to my local Lexus dealer and they suggested I needed a tow kit consisting of tranny cooler, larger radiator and towbar which when fitted would have cost 2k, if I had known this I would have brought the gs300. What I have done is fit an oil cooler which I sourced from Kenlowe for £100, I'm not changing the rad. but I've put some Wetter Water additive in the cooling system this helps lower engine temp. I hav'nt tried towing yet (I'm a summer caravanner) also waiting to have a towbar fitted,
a Brink detactable (£500 fitted )which is only towbar suitable other then a towbar from Lexus.
I'm enjoying the car, it's a far better car to drive than the Volvo but I'm only 19-23 mpg, 27 tops on a long motorway run.