If you haven't done so already I recommend looking at;
www.satelliteforcaravans.co.uk
Very informative site.
If you are taking your Sky+ box then my understanding is that to get full acces to all the + facilities then you need a double LNB.
I don't have one of the box kits but from what I've seen/read they seem to come with a receiver box,you wouldn't need that if you are taking your own. Also, agian only from what I've heard, the box kit only comes with a single LNB.
I take my own digi box with me (not Sky+, got to leave that at home) and bought a dish with folding arm and a tripod from one of the several ebay sellers who seem to specialise in this sort of thing. Think it was something like "gadgetshop" I got mine from. I got a 60cm dish with folding arm, LNB, sat finder, and 15m of cable and connections for well under £90 (was a couple of years back)
Might be worth having a look to see what's available and the prices.
Robert