
See these two threads for some photos link 1 and link 2
It is only a viable option if you do not have a stereo fitted in your car. You'd need to drill through the roll hoop and weld in a strenghtening plate to mount it in a VX. I've competed in Production class in hillclimbs and sprints with this set-up without any problem from the MSA scrutineers.
I had already removed the speakers, so Lotus fitted it through the speaker holes in the rear bulkhead panel (1st link). I later removed the rear bulkhead and foam soundproofing (2nd link).
£120 plus postage/courier costs.