Easy enough to install a front wheel chock if you like. I would not, just because I don't want to trip over it when the bike is out, or fool around with removing it. I would just tie it down with four straps. I've carried several bikes many miles that way in my trucks.
It's also true that occasionally the tires can move a bit sideways on rough roads and you have to watch for that. Or just add some straps to the bottom of the wheels to prevent it.
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