The tarp is a good idea. Others to consider
- Leave some junky stuff (broken baseball mitt, ratty clothes, etc.) on top.
- Check in early and park close to the main entrance. Typical thief will prefer minimal foot traffic.
- Take a northern route. It's freezing outside. Self-respecting vandals & thieves will be huddled inside for warmth.
- Choose hotels in lower crime areas.
- Put the highest value stuff in the trunk (if your car has one). Easier to smash a window and grab than to open the trunk.
- Oh, yeah: lock the car.
And, statistically, the chances of a problem are low. But not zero, so taking some basic precautions is reasonable. Good luck!