The most important thing you need to ensure, other that the obvious correct size, is the load rating of the tyres.
Your existing tyres have the index "95N", this 95 means the tyre is for a maximum load of 690 kg, and so the pair can carry 1380kg.
Make absolutely sure your vans Max permitted weight is no greater than this.
If the vans layout would in your opinion give an asymmetric loading allow for this in your selection. People talk about "ply ratings", these have no real relevance other that a description of the construction, though I feel the higher this is the stiffer the wall ought to be and this is no bad thing in a caravan tyre.
See this link for more ratings; http://www.blackcircles.com/general/sidewall
The N means it's a "van" tyre with a speed rating of 87 mph and thus an ideal tyre rating for use on a caravan. Being specifically a van tyre also implies that it ough to have a rugged construction, possibly featuring a "kerbing" ring on the side wall.
On speed ratings don't go less than 82 mph or you will be illegal on French Autoroutes, irrespective of what speed you are traveling.
The "S" rating one you have found is for 111 mph so speed wise is fine; just make sure that 95 load rating is comfortably adequate.