ME law allows for OPEN carry if don't want to get an out of state permit. While I know it is not always the best idea to advertise your firearm it is an option at your campsite etc. where it is most likely just your friends / family that are okay with carrying.
Note if it is not visible then it is concealed even in the vehicle. Ex: under the seat, glovebox, on the seat BUT cover by a jacket... At that point you either need a permit or it must be unloaded, no chambered round & an empty magazine. Best to keep ammo & firearm separate.
I have nothing to hide, am not a felon, and it's been a long time since I've done anything worse than speeding. If I'm stopped or approached by police I tell them I'm carrying open or concealed. Most appreciate the heads up. If my firearm is unloaded and stored away unless they ask I don't mention it.
While I would OC in the North Maine Woods, I wouldn't do it in, lets say, Portland or Kittery, etc.