Use a 6 or more channel receiver. Use channel 6 for flaps. You'll need a connector that allows two servos to plug into one channel without reversing. Use channel 1 for ailerons with a Y cable that reverses one servo.

Or, you could use channel for flaps, but you only get two settings: up and down. Then you can use channels 1 and 6 for ailerons that also act as spoilerons if you engage the airbrakes. Good for short landing rolls.