Sue
That's a bigun - from my experience you are going to need a large LWB 4x4 to get a safe pull and to make reasonable progress uphill. A Disco, Shogun, Landcruiser or Trooper would all do the job and have a kerbweight of around 2.25 tonne and a tow limit of over 3 tonne. The kerbweight is probably the more important figure as 1850kg trying to push you downhill on a motorway can get scary if you are not anchored in a big lump of motor.
Plenty of advice on this site about the merits of LPG - just to add my 3 penneth, if you don't need the room go for an internal tank; underslung make it more expensive and complex and in the case of a shogun reduce the petrol volume drastically.
Again from experience, if you are only going to use the beast as a towcar, consider a stonkin great diesel and make it Auto with cruise control, the only way to fly really - you will still get 20mpg and in Europe diesel is cheap as chips. Obviously if the car is an everyday driver then LPG makes sense.
Welcome to vanning and have lots of fun.
David