I can instruct you on sealing the spoiler area if its still leaking,
But stopping the leak won't eliminate the moisture already inside the car,
I know they work,
I've used them for car storage,
They trap the moisture then release it when out plug them in to a 240v mains supply socket,
They come with hangers that you can hang on the plastic hooks on either side of the boot compartment.
They will remove the trapped moisture from inside the car caused by the once leak you had.
OK, so I managed to retrieve the bulb holder which was somehow buried right down in the bottom corner. Seems to be working fine, although it is currently sporting a spare indicator bulb which is a bit on the dull side.
Regarding the leak after heavy rain especially overnight, there are visible water droplets on the carpet on the passenger side boot wall - would you expect this is coming from around the spoiler area mentioned above or could it potentially be coming through the light fitting or something?