go to homebase get a big role of ali flashing tape, its a think layer of ali with tar on the bottom (same as brown bread, do 3 layers of this on the floor, and 2 layers on either side, take the platic cover off of the boot lid, and get expanding foam with a long nozzle and spray it up either side of the lid, only do a small bit at a time as it will gush everywhere, box off the lock etc with cardboard and fill the rest of the boot with the foam, when dry shave and cut it as neat as possible, put some door draft excluder sticky foam stuff around the edge of the plastic part and put it back on, that will solve any boot rattles in the boot, but u will have to chase them round the rest of the car....