Did you try any on the "non-motoring convictions" list? If they aren't interested in non-motoring convictions, and they offer camper van insurance. I see that Aviva has a "specialist partner" offering camper van insurance, so maybe that would work out. Others on the list might be the same, so it has to be worth the effort, and if you can get both vehicles on one policy, so much the better.
As Chris Stacey said: Although its not formally part of the sentence that is handed down in court, the criminal record that someone comes away with effectively becomes a second sentence, which can have a long-lasting, if not lifelong, impact.