It really depends. Are the sides around the bottom or on top of it? If they are on the sides the bottom clamp will hold it in place. If they are on top of the bottom piece the weight of the glass will hold it, so long as once you place the glass you dont move it.
Braces can be added after everything else is in place and cured a bit.
Braces can be added after everything else is in place and cured a bit.