First, you cannot carry in Mayland, open or concealed, without a Maryland permit (which is impossible to get), unless you transport an unloaded and properly secured firearm according to 18 U.S.C. § 926A.
Second, as far as permits, you have multiple options. First, you should be able to apply for a PA LTCF by mail. There is no specific requirement in PA law that you apply in person. Also, you may apply for a Florida permit (proof of current military service will fulfill Florida's proof of training requirement), which will add Delaware to the list of states where you may carry concealed.