I have fixed down 4mm ply[sounds like i should have used 6mm] over t+g floorboards in my 3mx3m upstairs bathroom.I am about to fit new w/c,ceramic shower tray,sink unit[4 legs],skirting boards and threshold.Can I lay some sort of vinyl floor sheeting down and then silicone everything down on top of it ensuring a really good seal and avoid accurate trimming.If this can be done what type of sheeting [and glue?] should I use.