Van insurance - Living on a Houseboat

Any advice on this one please?

My husband and I live in a houseboat, and have no other residential address. Our post goes to a local canal centre who provide a post holding service for us, and a number of other boats... but they are registered as a business. We have no postal address for the boat itself, and we are not eligible to get one.

I have just sorted out my husband's van insurance for this year, after much angst and hoop jumping... only to have a phone call from them a week later to say that they may not be able to insure us because our residential address (the boat) is not the address on the insurance application (the canal centre, our postal address), and it flagged up because the canal centre is a business address. Our driving licences, and bank accounts, and all other accounts are registered at that address no problem, so obviously we can't put his mum's address down for the insurance... not sure where we go from here...

any suggestions...?