If your destination is a location in MD, you need to leave the firearm at home. The Federal law allowing the interstate transportation of firearms will cover you provided that you are traveling to a location that you are legally allowed to possess a firearm to another location where you can legally posses a firearm. Since your destination is in MD (where we cannot posses a firearm CC or OC) you are not covered by the Federal law on transportation. If you are going to MD, leave the firearm at home.
Sorry, but you are S.O.L. when going to MD.
There are few exceptions. If you are going to a shooting range or shooting sports gathering in MD, then that is different. Just casual visit to MD is difficult without running afoul of MD law.
Please see Maryland Annotated Code, Criminal Law, Title 4, Section 203
http://www.lexisnexis.com/hottopics/mdcode/
*EDIT* It seems that the link above does not take you to the MD Code.
Here is another link that directly takes you to the specific code.
http://mgaleg.maryland.gov/webmga/frmSt ... b=subject5
Chip