There are some half decent neo-seals around, but I think they have to be tighter to work effectively.
The thing is, it may well be an allergic reaction to the latex causing your rash, not merely friction. If this is the case, then neoprene is your only option, unless you can find somebody to make you some custom latex-free gaskets (they make latex-free surgical gloves, I'm sure some kind of material must exist...). This would probably be quite expensive though!
Nookie also do a good looking cag (
www.nookie.co.uk/zone/ ) although I've never seen it in action.
Failing that, perhaps you could try wearing something on your wrists under the latex?