plywood underlay- underlay underneath this?

[colinpost]

bathroom is now ready for lino/vinyl. Current floorboards have had a good sweep , are level(ish) and no nails protruding.
I wish to lay 6mm marine plywood over this. Do I need to but a 'foam 3mm underlay' between the plywood and floorboards or am I being too fussy ?!

 

[ree]

No marine ply necessary. Simply use 6mm ply if you wish.

Dont use any foam underlay or anything else below the ply.

FWIW: Make a template for a one piece sheet vinyl merely flopped down, and edge sealed with silicon (no stick down required) is your best way to go.