Anyone fitted one? Any advice? Does it use the same undertray or what modifications are needed?

I fitted one once - I think i had issues with the clearance of the Reg/rec so ended up cutting a chunk out of the seat unit - other than that though all the mounting points were in roughly the right place .
Oh yeah I used a foam pad for the seat instead of the oem seat - not sure there was enough room for it to fit.
Hope this helps :)
Smev