Hi

Certain companies such as Admiral do offer multiple insurance, however i would approach this with caution as no one insurer is good overall and cars and vans come into different categories one being domestic and another commercial which would impact on any premium more.

It would be wise for your son to look around for a good van insurance policy and start building up his own no claims discount in his own right, although this wont be cheap for the first couple of years it will benefit him in the longer term.