As above.
My spare wheel well was like a swimming pool, had to take the bungs out to drain it. Initially I found water was coming in from the OSR light seal. For the volume of water in the wheel well I wasn't convinced this was the source.
I replaced both rear light seals, had the bumper off, wasn't impressed by the state of the vent seals, replaced both of these also.
Still found water was coming in, in the end most of the water ingress was from the tailgate boot seal, re-sealed this.
Not leaked since