For the 6 ft lengths and the bottom of use 16mm (or your nearest equivalent) , add bracing to the bottom, the sides and bracing can be 12mm or 1/2". Before siliconing mask everything properly, clean with vinegar and ro water, dry with a long free cloth. Clean and dry before masking off! 2-3 people to lift the glass and silicone, use tape or clamps to hold it all together, quickly tool the silicone, let it cure for a day, drill you holes and job done enjoy!
Really not difficult at all.
Really not difficult at all.