I've been a diabetic for about 25 years, on a pump for about 10 years, and practicing Uechi-ryu for about 10 months. After some experimentation, the best solution that I've been able to come up with, for a class that is about 1.5 hours starting at 7:30 PM, is:
-eat "dinner" no later than 5:30 PM. I usually eat pretty light for this meal, about 30 grams of low glycemic carbs.
-reduce basal rate insulin delivery by 20% starting at 6:00 PM and lasting for 4 hours
-disconnect the pump entirely right before class
-check bloodsugar at least every half hour, more often if I feel like it's dropping (I usually end up checking 4 or more times)
-I bring a quart of orange juice to class, and generally get through about half of it. Sometimes more, sometimes less.
-eat a 20-30 grams of carb snack immediately after class, usually a Clif bar. I only bolus for these carbs if my bloodsugar immediately after class is >150 mg/dl
-always bring an extra infusion set/insulin in case my infusion set gets knocked out or loose during class (this has only happened once so far)
This works well for me about 90% of the time. The other 10%, I either have a series of lows during class, or I have a bloodsugar spike (>250 mg/dl) in the hour or two after class.
Over all, although it's pretty complex to work it in, practicing Uechi twice a week has improved my bloodsugar control and my health in general. The good effects of the strenuous exercise seem to linger for about 48 hours.
I'd recommend the book Pumping Insulin
for some good general guidelines on changing pump settings around exercise, and, of course, talk to your doctor.