Your Picc has a kerbweight of 1240 Kg. To stay within the 85% rule you should be looking at any caravan with a maximum (MTPLM) weight of 1054 Kg. Next, you buy a copy of Practical Caravan and look up the new caravan section towards the back. Highlight all the 4 berth caravans and then delete all the ones over 1054 Kg. You will then have a list of all the 4 berth vans that your car could tow. I realise these will all be new ones and you want a used one, but it will be a good guide. The alternative is get yourself off to a big dealer where you know there will be several hundred vans for sale. You don't have to buy there, but you are bound to see what you want under one roof. Trawling round the smaller dealerships with only 4 or 5 vans for sale can be very time consuming. Happy hunting.