G'day Neil,
I posted about this last year, because I needed to replace the old Bailey channels. What I ended up doing was, glue the bottom in only (Sikaflex), glue and screw the side and only screw the top. My reasoning was that the screws were rusting and so was the door top and Bailey channel. I made sure that the drain holes were not filled and that the glue did not inhibit water to flow through. I only screwed the top so that I might be able to remove the glass at a later stage if required. The screws I used were (I think) 8g x 10mm stainless steel pan heads. Next time I would use 6g instead, the 8g (all I had) were a bit big.

I don't know if this assists you or complicates things. Other than that all the best.

Nathan.