For the rudder servo I found a handy sized hatch which was a pretty easy cutout with a dremel reinforced wheel:
I glued in some mounting brackets on the inside to secure the door and also give some hold for an inside plate:
Measured up, cut and servo mounted. Where this is going is quite compact but the servo is held down will allen head screws so it can be removed with an angle key.
I need a longer servo arm so that is on order now. When that comes in I can finalise the 3mm link and test out my rudder.