when attaching mirrors to the scuttle, do you guys put anything behind the GRP to make it a bit stiffer

I was thinking of bonding a plate to the inside of the scuttle to keep it a bit more ridgid.

is it neccessary?

using ZZR1400 mirrors if it makes a difference

I'm using R1 mirrors and put a 3mm 1" x 3" plate behind mine just for a bit of support. Should be fine as the scuttle is quite thick anyhow.

HTH.

I made a little aluminium block (flat on one side, scuttle profile on other) to square off the inside of the scuttle, so the nut didn't dig into the scuttle.

I have all.al. plates on the inside with rivet nuts to suit the mirror fixings, work fine no serious vibration problems.

I have big alloy plates on the inside & carbon fibre plates on the outside all bolted through the scuttle it's really solid no vibrations or problems.