Thanks for your help and advice and for the private messages which also helped enormously.
In case anyone else finds it useful this is what I did in the end.
I went with the open ended FTDI Chip Interface Converter Cable which was £15 from RS as my TRT800 Transponder cable came with tails ready for connection.
http://uk.rs-online.com/web/p/kvm-mixed-cable-assemblies/6877828/From reading this thread and from other advice plus information from the cable Data Sheet (which can be downloaded) and from the Transponder manual the connections I had to solder were:-
Transponder Cable Black (Rx) to USB Cable (Tx) Orange
Transponder Shield (Ground) to USB Cable Black (Ground)
All very simple and finished off with heatshrink to make the finished cable assembly. Note: I did not have to download any drivers for the USB.
There is one more step on the PAW configuration page which has to be done and that is to set the appropriate USB port to “Funke Transponder”. I initially forgot to do this despite already being advised I needed to do it and it caused a fair bit of head scratching as to why I couldn’t see CSA on the traffic page. Changed the settings and voila.
Also check the transponder setup page to make sure you have set NMEA 4800 baud and you are in receipt of a valid GPS signal as evidenced by the POS field.
I have chosen to permanently install the PAW unit behind the dash panel with the ADSB aerial screw mounted on top of the wooden combing. To do this I first removed the base magnet so it can’t interfere with the compass then I moulded a rubber base from SUGRU which can be screwed down and works well (Photo attached.)
For the P3i aerial I made up an RG400 aerial extension cable and mounted it to the panel itself via a bulkhead coupling so it is still visible to the sky through the bubble canopy but stays pretty much out of my eyeline. (Photo attached)
Hope this is of help to someone.
Matt