You can have as many insurance policies as you want on the same item, claiming from more than one is when it's illegal. e.g. your household insurance probably covers some of the stuff covered by your caravan insurance.
"I put my caravan in for a service and was told that the floor had seperated from the walls of the van, probably caused by it being towed by a van."
Towing by a van has caused that? How does that happen then?