I have seen a nice setup that I plan on using in my next application.

As Bill suggests, a small magnet and piece of magnetic metal works great to hold the panel shut.

Put the magnet in the fuselage and the metal on the panel/hatch. In order to open the panel, have a larger (stronger) handheld magnet to pull panel/hatch open. A little trial & error should get the right hold and removal forces. You may want to cover the removal magnet with felt or something to protect airplane finish.

- George