You guys ask some valid questions. Here is my train of thought for those concerns.
The back of the motor box, once the firewall, has been removed. There are large air holes in the front directly in the air flow from the cowl openings and more on the side so some air movement will exist.
For normal flight, each motor will likely draw only 20-25amps so they will not produce any significant heat. Since the workload is shared between two motors and the plane is ridiculously overpowered, I expect little heating to occur.
If you watch the videos from either my "Part 2" review or the SKS NEAT Fair 2005 video, you will see that the Edge 540 was decently powered with only a single 5330 motor. Note that the video editor incorrectly said 4500 watts instead of 3500 watts but Tom Hunt got it right on the PA system in the background. The second motor power will only be needed on occasion for hovering and vertical pullouts. etc. For the most part, each motor will see only half the workload as before for normal flying and aerobatics.
Recall that my motor box is not just 1/4" plywood but 10 ply aircraft grade plywood. There is a huge difference. Aircraft grade plywood is like metal but without the weight which is why it is used in aircraft construction. The usage of special screwed in T-nuts does not weaken the wood around it like the normal prong type T-nuts.
I have a laser temperature probe that I can use on the motors during the test flights. I also will have the temperature strips on my BalancePro HD packs to see how hot they get after the flight. Temperature dots also come on the packs that trip during extreme temperatures above 160 degrees F and don't turn back like the strip will.
Now you guys got me all worked up for Springtime again!
Regards.