As Enoch says....
My tank / boot area will be open to the elements for the test, with a full top panel that has no opening on top of the rear tub, might install a boot at a later date
Fire extinguisher will go between the seats....after IVA, even tho its a safety device I,ve heard some builders having problems at IVA with sharp edges on the extinguisher
My own tank was bought off "fleabay" , holds 25 ltrs which should be good for about 120 miles or so, might be less on a track day
, its not to the book spec but for the price (£30 delivered ) it was too good not to, & it still leaves me all the space above the diff as "storage space"
cheers
andy