To roll the felt is pretty simple but there's a trick to it. If you were to just roll it on, there's a chance the front edges might fall through the baffle holes and interfere with the pellet path. 

1. Lay the mono-core about 2 inches from the bottom of the felt.

2. Take the bottom portion of the felt and wrap it over the mono-core until it lays flat touching the other side of the felt.

3. Next use your fingers to tuck the top felt piece under the mono-core, but make sure the top felt is still flat on the top felt.

4. Once its tightly snugged, start rolling the mono-core until everything is neatly wrapped.

5. From here you can slide it into the LDC cover. I would suggest though, use blue painter's tape to hold it in place. Makes it easier to slide in and out and also keep the felt tightly wrapped.