I do not practice in MN but since you are going on a long road trip which will doubtless take you into many states I can give a general answer to at least part of your question. If your primary concern is asset forfeiture you must contemplate doing something that would make that a possibility. On a failure to signal no cop is going to ask you to get out of the car unless his attention is drawn to something potentially illegal. If a situation which justifies seizing your assets arises you don't have too many defenses, especially if you are transporting contraband of some sort.
An office cannot expand a general traffic stop without specific articulable basis to suspect additional criminal activity. I'm not sure why you are concerned about forfeiture or why your travels are relevant. You should loss any property for a traffic violation.
First, you should always consult with an attorney in your State. The application of the law does differ between states and, as a result, experienced counsel is necessary.
Second, a seizure may be expanded only if the officer has a reasonable and articulable suspicion of particularized criminal activity to expand the stop. A review of all of the facts wpuld be required to determine if a challenge exists.
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Mr. Schaefer is correct that in Minnesota, police need a good reason to ask you to step out of your vehicle during a routine traffic stop. They can, for instance, ask you to step out of the vehicle for "officer safety" - that is, if they have a reason to believe there are weapons in the vehicle. In the same way, if they have a reason to think you might be armed, they can pat you down for weapons. However, absent some specific reason, they cannot order you out of your vehicle, nor can they ask for your consent to search you or your vehicle. In most other states, however, the police can ask you to step out of the vehicle during a routine traffic stop, but still cannot search the vehicle without some reason to believe that there is criminal activity going on, or without your consent.
As for asset forfeiture, police can in some circumstances seize your vehicle or things in your vehicle. Most often this occurs in conjunction with an arrest for a controlled substance (drug) crime or repeat-DWI offenders, but forfeiture laws, like search and seizure laws, will vary from state to state.
The bottom line, though, is this: It is never a good idea to refuse to follow a police officer's order. If you are stopped by police, you should make it clear that you do not consent to any searches, but if they order you to do something, you should do it, and contact an attorney in that state immediately if you feel your rights have been violated.