They love to get into every hole and crevice on my boat, but so far they have left my tractor alone. It's stored in a barn most of the time. Come to think of it, they've never been a problem on my truck and that stays outdoors all the time.
But man, on the boat, they are relentless. The boat has a lot of 1/4" and 3/8" drain fittings to drain cupholders, rod holders, etc, and the mud daubers will get into those from both ends. I have to snake them out multiple times during the summer. They also like getting into the outboard motor's coolant "pee" hole. That can actually be bad news, as coolant flow for the fuel injection pump passes through there. So I have to verify it is flowing every time I start the motor. If not, I keep a length of weed-whacker cord on the boat to snake out the coolant passage.