Thanks for the replies. I will try the scaffold bar thing before I make my decision.
I think I WILL go for the double electrics after reading lots about it. I have read somewhere that I need to also get a splitter or something to stop all the power draining from my car battery. I will have to discuss it with the towbar fitter I think.
I've been qouted from one guy £160, but I didn't know about single or double electrics at that point, and he didn't mention it. This guy was trying to sell me the detatchable one for £275.(again, not sure if this is single or double electrics).
Another guy said it would probably be ok to fit a standard one, and he would be able to tell me, just by looking at the setup of the sensors. He qouted £230 for double electrics I think.
My goodness, so many decisions. Why can't life be slightly simpler.