There was a flat plastic tray in mine and I'd strongly recommend leaving it in as it provides good protection from all sorts of rubbish thrown up from the road (it's not directly protected by the undertray). In my case I was only changing an 096 for another 096 though.096 will fit. There should be a plastic locating peg or strip in the bottom of the battery box. You can move it to a different position to accomodate different size batteries. To fit a 096 battery, you need to remove the plastic part.
Today removed my faithful Magneti Marelli 70Ah 450 CCA for a Varta Silver Dynamic 74Ah 750 CCA
That's me ready for -40°C then