need tips for air filter housing size reduction

anyone has any suggestions what i can replace the air filter housing i have on my 200tdi. its a funny set up as the whole truck was converted from series 2 to defender front. the filter housing was fitted on the roof but i adapted the roof and hoping to keep it low' profile so i don't want to put it back there but it does not seem to fit in the bay. is there an another type of filter i can use .. do you recommend filters without housing kinda thing at all?

I once knew a man who fitted a discovery 300ti air filter housing into the nearside front inner wing, actually looked a good job as there is a lot of dead space in there, probably an arse to change the filter, but he did it for space.