Just pick on the most god-awful habits that she hates, tell her they are many-fold worse in LM, and there you go. Mine cant stand the thought of all those sober sensible gentlemen, dressed sensibly, and behaving themselves. 
But she does like the cars.
I think you may have something there gibberish... I get away with the fact that her indoors doesn't do camping... throw in a few tails of sanitary woe and Bob is indeed married to your mothers sister.
...or "It's Franks Camper van and there's only room for the 5 of us lads, and another vehicle would simply cost us far too much on the ferry"
...or "Did I ever tell you what happened to Phil's misses's the year she braved it..."
...or "The initiation ceremony for the trip involves drinking 10 pints and stretching your scrote over your head...do that and you're in!"
...or "No. Now why aren't you in the kitchen."
...(if I tried that last one though, I wouldn't be able to complete the initiation ceremony either!!)
