Reed switch
I used the same reed switch van's provides for the main doors. I used cushion clamps and mounted the magnet in the door, and then the switch in the frame and wired it to the G3X to alert me when it's open.
And just because I could, I have it activate the baggage and interior lights when I open it through a cube relay. It was pretty easy in implementation that's pretty clean when done.
These are the only photos I could find, but hopefully you get the idea.
"Pardon the dust"