With the roof spars and blocking installed I cut out the window and vent holes with a small hand router and a 1/2″ flush trim bit. Do yourself a favor and make sure you are wearing a dust mask and eye protection.
Here you can see the headliner seam but it will be covered by the window trim ring.
A close up picture of the blocking below the last spar on the front of the teardrop. The headliner is secured by this final spar to the deck.
Using a belt sander I cleaned up the edges of the wall, blocking, and spars to get a crisp 90 degree angle for the outside skin later on.