My problem follows on from KEV0044's dual battery question.
I have an ARB air compressor fitted in the engine bay where the second battery would go and I've just signed up to have a dual battery system installed.

Any suggestions as to where I could put the compressor as a permament mount? I've got a CD stacker under the driver's seat so that's a no go. It might fit under the passenger seat but there is a compnent there already. Anybody know what this is?

I've looked at a different battery layout that Slunnie posted elsewhere but this required gel batteries which I can't afford.

As a last resort I'll have to put the compressor back in it's box which will just take up more space in the back.