Problems with ipad -- not waterproof, fragile, limited battery life and if hidden under a steel camper body the reception may be limited.
As an alternative, look at take a look at the GPS tracking units they make for dogs now. They are robust, water proof, usually a week long battery and are small enough to attach to a dog collar, so quite inconspicuous. They have apps that can alert you if your dog escapes.... so if fitted on a camper, could detect if the camper starts moving.
Here is an example of one but there are heaps of them now.
http://www.petbarn.com.au/pod-gps-pet-tracker.htmlAnd of course there are the products on here for tracking campers etc.