I've used that injector. Be very careful and do not leave it attached to the keg. Otherwise, someone will decide the keg needs more pressure, over do it and blow the relief. It's really exciting the first time.
I've transported kegs on their sides and haven't had a problem. Since you have a long trip, get it as cold as possible before leaving.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
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