We now have a number of rides on the new belt. I tried to follow the instructions as closely as possible in the installation.
After a couple of rides, the belt started slipping under heavy pressure. It first did it on the same hill where the first belt broke. At first I wasn't sure that it was in fact the belt skipping, but when it became more frequent, you could see that the captain's crankset was advancing, and at the end of a ride where it skipped multiple times,the captains pedals were about 60 degrees advanced.
The belt tension was reasonably snug, certainly tighter than you would typically run a timing chain. In talkin with Web Cyclerly they suggested upping the tension, so I tightend the belt pretty much as tight as I could.
The tightening stopped the skipping, but lead to a substantial amount of noise. So I backed off the tension, noise disappeared, but it skipped again. Right now we're back to very tight, noisy, and no skipping.
I'm going to try reversing the belt direction as suggested in another thread.
I'm concerned at this point that the violent skipping under pressure may have damaged the belt (given that they can apparently break from just being rolled on the ring) And the noise level is really not acceptable.
So for us the belt is an ongoing saga. And I'm beginning to see why Co-Motion does not reccomend retrofitting them.