primer for sikaflex 252 to bond ply battens to floor?

Hi
I've cut out 9mm ply battens for the low points in my 17 Reg T6 floor. I'm planning to stick them to the metal with sikaflex 252. I'm planning on giving the floor a really good clean first. The painted metal surface is in good nick. Do I need to use a primer before using the sikaflex?

After bonding the ply battens I was going to fill remaining gaps with closed cell foam, and top it all with 12mm birch ply screwed into the 9mm ply. I am thinking of using 2 or 3mm extruded polystyrene (acoustalay 300) just under the birch ply to try and reduce cold bridging from the raised metal ribs which will be in contact with the top layer of birch ply. I'm concerned that this could deform over time threatening the security of the RIB bed/leaving a gap under the furniture. Am I being paranoid?

any wisdom would be appreciated
thanks
 
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