Amazon's recently experiences with sales tax collection shows that a motivated government will keep its eye out for "business presence" and then regulate when it becomes politically useful. Freedom's just another word for something too small to bother regulating.
On another note, states already have rules dealing with buying a car in another state, so it is settled law.
When Amazon was "just" an online "catalog", it could take advantage of cases like Quill Corp, which held that a catalog with no physical presence in a state and which sold few goods into that state did not have sufficient nexus to establish the state's jurisdiction to tax.
However, Amazon is the single largest retailer by volume in nearly every state in America, topped only by Walmart. It sells a substantial volume of goods into every single state. Legal commentators, including numerous former SCOTUS law clerks, have noted that if Amazon were to challenge state sales taxation today, it would lose because the justification set forth in Quill does not apply. And that's with a significantly more conservative/libertarian SCOTUS than in Quill.
Transit through a state is not considered a business or a business activity, hence the trucking company could not be regulated. It could be different for a travel company, but in such case that would be services income which is not subject to a sales tax.
With a travel company, the distinction is that the journey is as much a part of the business activity as reaching the destination.