89 Ford Maverick/Nissan Patrol rust hot spots

Attention all Maverick/Patrol 1989 on onwards- just wondering if anyone else from experience knows where any rust spots are likely to develop/or have developed in order to prevent this car cancer ruining the vechicle!

The reason I ask this is that when I went to rewire the speakers in the front doors of the 4wd, behind the trim in both the passenger and driver door on the inside bottom right corner (for passenger) and inside bottom left corner (for the driver door) there were two rust spots about the size of a tennis ball (beleived to be that the rust began as when the reinforcing plate behind the metal which helps brace the bottom hinge was either not rust treated/painted etc in between the 2 surfaces and rusted from the inside out!)

Under normal conditions (i.e. not re-wiring a speaker system) it would never cause most people to take off the trim of the door for the fun of it, and no rust is visible on the external parts of the doors! So if you have looked, I suggest you do. (The whole trim doesn't have to come off with the internal door handle. window winder, etc - just pull off the bottom corner of the trim (closest to the cabin)) Also check if you have had anyone else in the past install new speakers in the doors to check the holes they drilled for the screws as well, most of them were rusted out too!