Sum,
We plan on using two chutes. The primary chute is in the back behind the rear end. The secondary chute is in front of the rear end.
You are correct about the location of the tether point. The tethers exit the body through the primary chute door opening. This mean that if I accidentally deploy secondary chute first it will smash the primary door.
The secondary door is shaped like fly swatter.
The handle of the fly swatter is what let's the riser come through the body work between the two boxes. I can make you a video of how this works if the weather warms s bit. Right now the car is under 6" of snow.
I studied your design for a bit . Why would you want to change what you have. It looks pretty good to me. Are you contend about the drogue chutes clearing the doors?