I purchased a new, deep 2” hole saw for this and I’m glad I did because it made drilling through the fiberglass and foam core very easy. Here’s the hole, elongated as per the instructions.
Drilled out wing attach bolt access holes.
Access hole shown opposite the actual bolt hole on the spar.
This process has to be completed on both sides of the wing. After the holes are drilled, they need to be reinforced with a couple of layers of BID
Reinforced bolt access hole.
The whitish spots come from sanding down the strips of BID.