Not sure about the turbo tunnel, but...I'm in a similar situation using a 9'8".
Tips when not using the turbo tunnel...
I'm not sure about you board positioning. From what you wrote you may need to move back a little. However, you may just need to sit a little deeper and paddle a little sooner. I've had the same problem on waves that I tried to take off on too late. You probably just need to get into the waves earlier. It seems to me that everything involved with longboarding takes more time. Such as starting your turns earlier and ending them earlier as well. My first real "successful" bottom turn carried me right off the top of the wave

. When you find yourself a little inside on waves that might be a little bigger or jack up on you, try angling more on the take-off to help prevent your pearling problem.