Give Alex a ring at Custom Divers (01737 773000). He's very helpful and willing to spend time answering your questions. Only thing is he will probably recommend a CD backplate and harness.
If he does, and thats the way you decide to go, don't buy it direct from CD, go to someone like SDS. You WILL get it cheaper. EG Remote isolator from CD £96+£10 P&P=£106. from SDS £83+£4 P&P=£87.
Alex gets the sale indirectly (ie the shop have to replace what you buy) but you end up paying less .
Dive safe
Darren
PS You'll probably find you get a better response if you give your real name somewhere in your post/profile.