Motorhome rental near Calais

I have been asked to find / recommend places that hire motorhomes / camping cars near Calais for friends coming over for the LeMans Classic in late June. They will need two vehicles, something big enough to be able to leave the double bed in place during the day so something bigger than a converted VW van. I live in the south so don't know the area at all but I know some of you live in the frozen north and would very much appreciate the benefit of your collected wisdom, knowledge and experience. Thank you in advance.