Hi Rodney,
I can speak only for the 2010 XF 3 litre petrol version and I don't know if you have the same body layout. With my car, if you remove the felt lining to the spare wheel space and also the felt battery cover you have enough room for a full sized spare tyre with the boot floor fitting OK on top.
Like you, I was unhappy with the goo and pump.
Tony.