I think a few of us have been down this road. 4 Cyl car but want an Expanda, get a Swan instead, cars still a bit of a struggle, get a bigger car, buy and Expanda, sell the Swan etc. My advise would be to not undercook the tow vehicle. It takes a fair bit of fun away struggling down the highway burning tonnes of fuel. We've been through two cars until I felt comfortable! We've now got a Triton dual cab which we love, throw the bbq, bikes, boogie boards in the tub, hitch up and off ya go! Could be worth looking at the Caravan Association towing Guide (its on here somewhere under technical I think). That lists each vehicle and its tow rating. But for a 17-18 foot Expanda you'll be wanting a turbo diesel ute or 4wd really I'd guess. Good luck!