Personally, if I was looking for something a bit different, I would love an American van, you can get them with v8 petrol, usually about 5.7-6 litres or turbo diesel as big as 7.4 litres!. Or, how about a v8 pickup (ute) from Australia, a Holden ss has a 6 litre v8, same as you will get in a corvette!. Seriously though, with the road tax rates for commercials, and pre march 2006 vehicles as they are, if you don't cover a lot of miles, might be worth looking into something with a lot of grunt. I would always be wary of putting a water tank in a passenger car though, for the reasons I mentioned. I'm not saying it couldn't be done, but you would have to be very aware of the weight limits, safety aspect, both with regards to securing the tank properly, and how putting a large tank of water right at the back will affect the handling as the weight distribution will be severely affected. If memory serves, a bmw x5 has pretty near 50:50 weight distribution, so even a 250l tank behind the rear seats, is going to change that dramatically, maybe as far as 35:65 f-r, which would result in very wayward handling!. Just in case anyone is actually thinking about it with the beemer, according to autotrader, the gvw of the 4.8 is 2700kg, and the minimum kerbweight is 2200kg.