Newbie help with purchase?

So my partner and I have decided to take the plung and get a caravan.  We've just change our car to a Range Rover Sport so we think we have the right Tow vehicle for most options we are considering.   We both want a fixed bed, and like the layout of the larger twin axle Sterling 645.  However I keep getting told there could be problems with owning a twin axle around getting access to sites and additional charges.  Reading the forum there is some discussion around this, and it seems that this isn't really a problem if you call in advance and confirm with the site.  So any advice on the twin vs single would be helpful.

Secondly, we are planning to head to NEC in October with the intention of maybe buy one, I can see some people commenting that they have brough at the show before, so any advice on the best way to do this, as I'm concerned we'll get some pushy salesment that could put us off the whole idea.

Thanks for any help...