My recessed shower has a very small "inset" at the front, where I'm going to have to put tiles - about 2." I'm going to use a metal outside corner, but the backerboard will not be supported by very much, around 1" of furring then it's going to cantilever over the shower nailing fin, which is around an inch also.

I was considering putting a bead or just blobs of mould-resistant silicone or caulk under the unsupported edge of the backerboard, to give it some cushioning and stability, and perhaps silicone between the backerboard and shower itself, which will be covered by the tile. Is this a good idea?