Now the pieces to be used using 2 fortees :
Then mount a part of the fort in the traditional way:
From this point, two options can be made.
A) You can use the two parts of the ports, getting your fort with two entrances, or sanding to fill one of the parts with plastic mass.
In that option, it will imply that you reduce the size of the opposite wall to have symmetry, causing a small reduction in the size of the fort :
Option B) This is what I'm going to do.
I will use the other wall, bigger and fill the gap by cutting and gluing a part of the part of one of the doors that fits the building:
Regards.