Just did this...didn't take too long. With a cold air intake, you don't even have to remove it, and can just remove the screws and leave the connectors attached to the blower and resistor.
I was still surprised at how much stuff there was in there, and that it hadn't started a fire in all these years. There were pine needles in the resistor wires, and lots of leaves. Maybe not a lot considering it's never been cleaned since it was new.
Maybe the Ford engineers put the resistor there with the intent it would burn up such debris? Seems to have worked that way on mine, there was a lot of small burnt up bits under the resistor. If rain water gets in there and washes them down a drain exit, it could work.
Be careful when poking around in there though, I messed up some of the evaporator's fins with the vacuum hose tip trying to get all the small stuff in the bottom. A smaller flexible hose taped to the vacuum hose would have worked better and probably not messed up the fins.