Reply to "Stopping rain etc getting in through rear deck lid aperture"

The distributor boot was included on the Mustang GT 302 starting around the 81 or 82 model year.

while it is designed to keep water off of and out of the distributor, the cap and the cap wire connections, it is also notorious for retaining moisture within it from condensation.

The simplest solution is to use the '74 production engine cover that had the solid center added to it to cover the air cleaner to prevent water entering the air cleaner/carburetor assembly.

The early all wire mesh cover looks much better but there were waranty claims where the engine needed to be replaced because water was leaking into the carburetor and then the engine and the engine can't compress liquid water, so some engines were damaged with bent connecting rods as a result.

The fix was the 74 production engine cover with the solid center.

If you drive your car, it is not possible to eliminate the dust or rain being sucked into the engine compartment from under the car. That's part of the design of a mid engine car to help cool it. You can only reduce the infiltration to a degree with the 74 engine cover.