Not too long ago we were stopped by MD troopers. The excuse was "interdiction program". They asked if we had any contraband such as drugs, weapons or bulk tobacco products. Then ran our plates and told us the vehicle was reported as stolen. After a lecture on how we need to contact DE DMV he let us go. When we called DMV they said that the MD troopers are always pulling that crap.
An amazingly beautiful state but poison fruit. Just like Jersey.
That's a tough one. If you have a gun even if carried legally, and say yes they may want to search the car. Of course this would be refused but they may take the position that the presence of a gun gives them the right. I would bet you would at least hAve the gun confiscated and probably spend the night in jail.
On the other hand if you say no, and they search anyway, would be charged with obstruction of justice.
Best to avoid that state.
I have traveled throughout the USA and compared to other states I do not find Maryland all that beautiful except the bay, eastern shore and the mountains. Rest of it is pretty mundane suburban sprawl not worth seeing.