Hi All
Here are some photos of the Boots on my Pattern 12 these are not based on anything other than the need to cut down on the hot air coming into the cab area from the engine.
The starter boot is held in place by simply sewing a length of stiff plastic tubing made into a loop in the bottom of the boot, which is squeezed through the opening and then expands.
Excuse the pine needles in the Pattern 12, such is life for a open cab truck even when parked out for short periods of time it collects leaves and needles.
Looking at the remains of the felt under the plate for the starter and parking brake on my HUP it had the simple felt closure on the holes. The felt must have been 1/2 to 5/8ths thick originally.
Cheers Phil