I really don't think you need to worry about it being cool enough in the summer in Maryland. Since you plan on living in a structure with 2-3 inch thick walls in the north during winter, keeping warm should be on your mind. You will use a lot of propane and face heavy condensation inside.
I camp in the Florida heat all summer long. My ducted 13500 btu AC keeps my TT ice cold if I want it to be. We leave our pooch when necessary in a canvas crate that is collapsible - and before getting jumped on, yes has screen windows for ventilation.
So my advice it to think through wintering in a TT as well.