You mean just mounting APM?
I used 1/4" balsa and cut two pieces and glued them to the sides of the compartment, then I put some vibration dampening rubber stuff (like for mounting heli gyros) on top of them and put a shelf on top. Then I put the APM on more vibration dampening stuff and rubber banded it onto notches cut in the shelf.
I put the compass all the way to the back of the plane, and embedded the airspeed about a foot out on the wing (at the apex of the A on "apprentice")
There's no good way to mount a camera, but as an experiment I mounted one of the little 808 cameras on a micro servo pointing straight down. The micro servo does an excellent job counteracting roll, but there's too much vibration from the motor.
Looks great, thanks. See what I did for the camera (Gopro Hero 2) glued the camera base support on the bottom( battery compartment) and use couple rubber band to hold it in place. To get little more clearance from the ground I bent the landing gear frame and also adjusted the nose wheel. I am very happy with the results.