Unless you have a MD-issues permit, carry is illegal--OC, CC, carry in your car, even transporting it in most situations is illegal.
If you own property (home or business) in MD, you can transport a firearm between your home and that other property in your vehicle. You can transport a gun from your home to a range, gun store, gunsmith, or official event (like a competition), but you must NOT go anywhere else, or make a side trip while transporting your gun.
You may transport a firearm THROUGH Maryland per the Firearms Owner Protection Act (FOPA), but it must be unloaded, locked in a box, the ammo stored separately, and inaccessible by the driver or any passengers.
Essentially, if you own a gun and live outside of MD, and don't own property in MD, the best way to deal with MD gun laws is to AVOID Maryland, because there is simply NO legal way for you to transport a firearm into MD unless you are taking it directly to an event, range, smith, or gun shop, and then going directly back home.
IF you are vacationing in MD, there is almost NO WAY you could legally have a gun with you, unless you are a cop and covered under LEOSA-96, and even then, some jurisdictions may try to arrest you for illegal carry anyway, because in MD, they seem to believe that Federal law doesn't apply to them...
Good luck... I'd suggest vacationing in WV or PA...