My apologies for not specifying the F-48 size versus the 1 meter size.

Although I do use the same diameter carbon cross beams on my 1 Meter multi only because I had a bunch of tubes already purchased. On that one, I too use tape wrapped around carbon tube for locating left/right location on main hull and as "stops" for float attachments. The carbon tubes are held inside the glass tubes on top of the floats by the rigging. Mirror hanger are screwed to outside of the tube (wood dowel inside) to which the "Y" harness for side shroud rigging is connected. Hopefully photo will help explaining this method. It is a glass tube mounted tot op of float into which the carbon tube is inserted. A small wooden dowel is pressed inside the carbon tube and the hanger is screwed to the wood.

Cheers