Hi I was in a similar position to you. After using all the online search engines I could only get a quote for SDP (no commuting) or business. I phoned the best quote to check and they advised me they would look into why this was not an option online to add SDP&C. I took out a SDP only and simply added on commuting to a single place of work for an additional £30. I checked about the need for business insurance etc with it being a van and was advised there was no need. Yes your insuring a commercial vehicle which some insurers will not insure but no need for business insurance (but do double check with who ever you go with). I ended up cancelling that insurance as I was not allowed to add additional Windows and seats so went with a broker and a modification friendly policy.
Good luck
Phil
Good luck
Phil