I still had some slight differential flexure between the RH200 and the camera. This only showed up on long exposures of sixteen minutes plus.
With the guidescope near the top of the camera it shows up as rotation and star elongation at the 'top' of the image which is really the 'bottom' of the camera.
I moved the guidescope to the centre right of the camera. For test purposes I ran some cable ties to the top of the RH200 from both sideplates.
It worked!
NGC6188 4x16 minutes in NII. Large image here 5MB.
http://d1355990.i49.quadrahosting.co...GC6188_NII.jpg
I will get a couple of stainless steel turnbuckles today to replace the cable ties.
Bert