This is how I did it
1. Glue Batons
2. sound deadening
3. insulation 6mm hard sheeting
4. 12mm ply sheeting fixed to rails with Countersunk M8 threaded, which I know is not what your doing,
however, there is no right or wrong way, I did this way due to running cables and possibly need access again in the future...
good luck with your build
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