Well, whilst I am no expert, I think the obvious thing to point out is that due to their age, you really need to find one which has been very well looked after or well restored as they can be unreliable and the last thing you would want is for one which isn't going to complete the trip. This will also mean you are going to be paying more, as many people will buy one which isn't in great condition at a low price and restore it themselves, but it doesn't sound like your in the situation to do this!! People have done so much work on this things, like making newer models look like the retro ones, that as your not a collector or having it as a hobby, I wouldn't worry too much about models and such. Just have a look on ebay and auto trader, which is where you'll find loads advertised, this will show you whats available, just use google to read up on them a bit, theres sure to be hundreads of forums out there and then you can get the van most suited to you for the right price. The links are
http://www.autotrader.co.uk/ and
www.ebay.co.uk. I hope that helps even if it isn't very specific, but like I said i'm no expert.