Think I've sussed a way round it now. I have a flat tank and can partition the floor with protekta coat from the tank to the tailgate using a divider.
Seal all around the wheel arch covers, and up to the divider. As only the rear of the floor really gets water on it, drips from brushes and hose reel etc: I think this could work out OK.
Until I leave the water on when filling the tank
Thanks for the advice all. Including Mr Warford the Dude
Wayne