If this person has a wife/girlfriend/buddy whom you could enlist to get the message across, that may be effective. Otherwise, you may have to be direct, and tell him that the odor is unpleasant and you simply can't see sharing a camper with the smell. Not the sort of conversation most of us look forward to, but it's do that or suffer.

Of course, I rather like Spaw's "it's not the smell, it's the eyes burning" line.