On my Staggerwing build i have a "door" on one side. There i just cut 3 sides, and last side (top) just trough the foam, not outside paper. And used a bit of wire square "U" shaped, one leg on outside,other inside in same angle.
If a hatch, normally i make a foamboard bit, or popsickle stick stick out in front to fit exact under skin in front of hatch to makethe hatch level with the fuselage outside, magnet or velcro in rear. Some, just velcro in both ends of hatch.