The XL has an offset spring hinge so installation is different than the large.
Fill the BGE with charcoal - 600-700F cooking consumes charcoal faster than a regular cook.
Start by placing the plate setter with legs down. Make sure one of the legs is positioned toward the front. The plate setter does not have to sit down in the notches of the fire ring. Then, place the cooking grate to separate the hot plate setter from the pizza stone. Additional spacers can be placed here. I choose to place an additional deflector under the pizza stone - in this case an aluminum deflector. Then, place the pizza stone. I recommend the 14" stone on the XL as the larger stone extends beyond the plate setter and blocks a great deal of heat. If you have the XL stone, make sure to space it up above the felt line to allow heat to flow around the edge.
Set the Pizza-Porta on the base of the grill positioned slightly offset toward the front (1/2"). Lower the dome. Just before the dome is fully closed push the Pizza-Porta toward the rear, positioning it left and right at the same time to center. The top metal tabs should be inside the dome allowing it to close tightly around the perimeter. The rear of the Pizza-Porta does have some flex designed in so it may be a bit tight on first fitting.
The hinges of the BGE allow some variability in their adjustment, and they can drift with usage. Sometimes dealers even get the hinge too high or low. If the Pizza-Porta does not fit as described above, ensure that the hinge is 10mm apart all the way around and that it is centered between the top and bottom. Follow the BGE instructions for adjustment procedure. Tighten the bolts regularly.