check on your own insurance - some insurance companies have a value that can be set against your student son's property whilst he is at uni - and it does not increase your own policy cost - i am with direct line and it is included with them but you have to ask so they can mark it in their records
our insurer does cover my sons goods even though he has never been in halls, always privately rented - it is worth asking around the insurance companies because quite a few do this but don't tell you unless you push not any use to you now but a thought for the future
DD's stuff was covered on our policy whilst in hall. She's moving into a privately rented flat now so a policy with Endsleigh is the best value - covers legal disputes with landlord and, for extra, insures a couple of valuable musical instruments. It works out at £12 a month all told including the instrument insurance. She and her flatmates might ultimately be better off getting a housesharers' policy but that was too complicated to do long-distance this year.