Water in spare wheel well in 2008 TDI Sport saloon

[CRG23]

I'm continually emptying water from the bottom of the spare wheel housing in the boot of my Passat. I've had a new boot seal fitted, and the drain channels cleaned out by a VW technician, but the problem has returned worse than ever. None of the material boot liner is damp, apart from a very small section at the bottom offside corner where the lid closes. I've already emptied it twice since Friday, it's now Monday, so any suggestions/ideas would be very welcome!