ive never run a half marathon, but i am on my university's cross country team, and ive been running for close to 8 years now (i started in middle schhol). Some of my training runs have been close to 13 miles (half marathon distance)...my longest races however are only 5ks.
In order to prepare for a run, i find it is really helpful to drop my basal rate 2 hours before i plan to run. for example, if i plan to run at 4pm, i drop my basal rate at 2pm from .95/hr to .45/hr. this way, by the time im ready to run, my blood sugar will be at my pre-run target of 170, and i wont need to eat a lot of extra carbs. i also have a post run basal rate set to acconut for the 8 hour post-exercise lag.
i find that i tend to get low during a run if have insulin "left over" from a previous bolus. for example, if i go running right when the insulin is peaking, im almost guranteed to get low. because of this i try not to bolus (for food) close to the time im going to workout. i will however give myself insulin to correct for highs, but even those corrections are modified.
also, because of the early morning insulin resistance, i find that i can have a lower pre-run target in the morning, but if i dont take any insulin before a morning run, i tend to get high. because of this, i try to have a small breakfast/snack before working out and i give myself a modified bolus.
good luck in the half marathon! once im out of college (and no longer on the cross counrty team) i hope to run a marathon. i need to start looking into marathon training...
BEST OF LUCK!