Very interesting stuff!
"The airframes of modern aircraft are primarily constructed from aluminium alloys which are non-magnetic; the main potential magnetic sources are the engines. As a first approach, then, magnetometer sensors have always been mounted as far away as possible from the aircraft engines."
In an armored car the whole vehicle is a magnetic source, alas.
"Permanent magnetisation of the aircraft which will be unchanging unless engines are changed or magnetic objects (such as toolboxes) are brought on board."
Not sure how the Project avoids that. Careful with re-arranging your machine guns!
Finding the base itself (which has thousands of tons of rebar and structural steel) will make finding the actual entrance much easier. Keep in mind that whatever capabilities you describe for the Project magnetic sensor will be brought up again by your teams!
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Michael B.