I'm re-installing my new rear subframe (for the 5th time) and upon referencing my photos of the old one, I remembered that there was some felt pads between the boot floor and the subframe. It seemed to me that these were a pretty good moisture-catcher so I didn't replace them. Before I button this subframe up for good, I thought I had better seek the advice of the braintrust and see if the pads are needed (and what they are there for?)
The felt pads did encourage rust, but the subframes rusted else where quicker than under the felt pads.
In later years the 3 felt pads were replace by 5mm thick rubber pads. Personaly I would recomend fitting rubber pads. The reason is on some cars the subframe will touch the boot floor.
They are glued on to the subframe, positioned over the triangular recessed shape on the top of the web.
The other point to mention here is remember to block off the access holes on the front cross member with canvas tape, to stop muck getting in before you fit the subframe.