Mouse proofing.

We had mice in the caravan during one winter.  They chewed holes in sleeping bags and other fabric items.  Luckily none of the caravan upholstery was chewed, even more luckily, they didn't chew any electric wiring.  I made the caravan mouse-proof by covering the air vents with fine mesh.  The vents already had plastic mesh over them but as, I'm told, a mouse can get through any hole that a pencil can get through, the holes needed to be smaller.  The problem of course is that the vents are a safety feature and must not be blocked.  My solution was to buy a sheet of metal mesh from a garden centre (cost about a fiver).  For each vent I cut a rectangular piece of mesh, folded it in half so that the mesh size was effectively halved and was too small for a mouse to get through.  Then, using a strong stapler, I simply stapled the folded mesh over the existing vent holes.  This was all underneath the caravan and out of sight.  Result, no more mice during winter storage.  As an added check I left a small fragment of biscuit in the middle of the floor, if any mice got in they would certainly have eaten it and the missing biscuit would have told me that more mouse-proofing was needed, the biscuit was never touched.  What are your mouse-proofing tips?