Its been a few years but there wasn't anything special about the drilling both skins and the wedge.
One recommendation is to use some material on the backside of the wedge as a guide when countersinking. As you CS the 'other' side of the hole the CS bit will start to wander and chatter because as the 2 countersinks meet the hole enlarges. Hard to describe, easy to see.
I purchase 2 sections of 3/4 in aluminum U channel from Lowes. I clamped each one to a skin and match drilled them. After you have match drilled the skins and the wedge, remove the wedge from the skins and cleco it to the u-channel. Now the CS bit will have a pilot hole to follow.
You can then use both the sections of u-channel while pro-sealing the wedge to the skins. This will prevent pillowing and keeps the training edge very straight. Since making the u-channels mine have been used on 2 other area RVs. See Mikes website (link below), he used the channels I made and documented how he did it.
