I am about to pull out our old bathroom suite including a shower cubical and tray. The existing tray is acrylic and was installed on a riser kit. The replacement we've purchased is a low profile stone resin tray. The bathroom subfloor is chipboard tongue and grove panelling. I've not installed a resin trays before. Am i supposed to lay a bed of mortar/cement between the tray and subfloor or can the tray sit directly on the subfloor?