I know this is a thread resurrection, but just to add my 2p worth...
While the boot space in the Cayman is suited to soft luggage, I have found that the available space to be "vast".
The wife and I did a 3 week trip to Spain a couple of years back and the boots were big enough for the task:
Clothing for 2: We took about a week's worth of clothes each and washed as needed.
2 Full Face Crash Helmets : Did a track day at Guadix
25 Bottles of Wine : We stopped in the Rioja region on the way back and loaded up.
Computer/Cameras/Video/etc to keep me entertained while on the road and track.
As long as you pack/think with care, you should be fine

HTH