Not for the spacer itself you dont, although I will need to find some way to seal the centre 6 bolts to stop them sucking air.
Normally done with nylon spacers.
mmm my pure plenum kit came with the middle gasket to help with the nylon spacer's keeping tight in the middle, do think you might get air sucked up (down really) from the 6 middle bolts otherwise?, some DYI gasket on tube might sort that though.