Anyone Have A Recommened Compartment Door Mod?

ChanW said:

Jill, I cheated by drilling through the wall from the inside, to install an outdoor 12v plug. Then I could figure out the measurements to outside trim edges etc.

Yup yup, like a small "where am I" hole. I need a non destructive way to get the max dimensions. May try from edge of hot water heater. Or maybe a strong magnet to with a screw?