If you are going to use an RC servo to control the door, then the RC model aircraft world has all sorts of RC servo attachments and accessories. You could possibly attach a control horn to the outside of the bottom door (similar to ones used on RC aircraft control surfaces etc). You could then run a push rod to a bell crank (I think that's what they are called to change the direction by 90 deg to a second push rod running up the outside of your chamber to your RC servo.