If you have a gun in MA, keep it out of sight. You don’t have to declare unless the cop asks. Don’t leave it in the glove box. It should be either locked in the trunk or “under your direct control” if you are transiting. Unless you are speeding, or driving a shit box, your chances of getting stopped are slight.
Really, 90% of the advice you are getting is from people who don’t live here. The weather is great. The natives are peaceful. Unless you are buying crack it’s safe. Pot is legal. Guns—outside of Boston, are unseen but common.
Don’t go to Cambridge or inside of 495 and life is pretty good, fairly rural.
There are liberals—but they aren’t in you face unless you want to “get into it.” We get along fine.
Massachusetts is one of the worse states to get caught with an out of state handgun (along with New Jersey). Massachusetts does not honor any out of state CCW permit and has been know to be very harsh on those caught believing they were safe with their papers.
Without an MA permit, you are not permitted to carry in a vehicle, carry at rest stops, or carry in state parks. You also cannot carry any firearm with more than 10 rounds.
Best to drive around...