[Chris Burkard]

Do not use screws. They will pull out if the rail is actually used in an emergency situation. Welding would be best, but will require stripping the frame where the welding will occur and then repainting afterwards. Thru-bolting would work, but you need to determine what is inside the frame and where the edge of the glass is. As aksmith said, the glass may not leave you enough room to drill through. You will have to do some disassembly to see what you have to work with.

Good Luck,