What the best way to stop floorboards squeeking

Mine squeeked and flexed a lot. Had to lift them all to clean bilges, fitted new bearers(they were soaked in diesel) + extra stiffeners in 'flexing' areas, extra screws and now no squeeking. Also added more opening floor hatches to get at bilge.
 
I have used self-adhesive velcro to hold down all my floorboards. No squeaking, can get them up in a hurry, and in the hopefully never experienced scenario of a rollover they should stay in place.
 
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