While watching football yesterday and thinking about Ned's comments, I decided to take a look at mounting the quad ESCs. It turned out to be so simple that I completed it.
I slightly enlarged the opening below the carbon tube so that an ESC could pass through it. It made for an easy plug-in-test setup so that I could test the rotation with a spare R/C system. I often use my old Spektrum radio for this and then use my FrSky Taranis for the actual flying radio system. I'm using an H-frame and labeled the ESC control wires 5-8 appropriately. Since my ESC to motor connections used the triple 3.5mm shells, it was easy to reverse the motor direction by simply unplugging the connector and turning one end 180 degrees.
The ESC wires were covered on the fuselage bottom with white duct tape. It's strong and sticky so it won't come off. Notice that I also covered the fuselage center with the same tape. I'll give the boom bottom a finished look later in the project.
The ESC power wires were joined together with 4mm Male to 3.5mm Female Adapters from HK. The 4mm bullets will mate into my final 4mm Bullet-connector harness. Note the intended position for the Forward Flight ESC so the air flow comes from the bottom of the image and passes through all the ESCs (and FF motor) on its way out.
Lastly, it looks like the top hatch is so big that the Pixhawk will easily mount on the plywood tray (with a vibration dampener) and still have plenty of room on top for wires without hitting the hatch. It looks like more than an inch gap.