Al,
For your longer rides definitely consider bibs. No matter how well your shorts fit the chamois is going to move around especially in hot, sweaty conditions. The bibs will last a long time if you only use them on longer rides. Do a search and you'll get lots of opinions, but there are good values out there that folks seem to find work really well. I've got both Giordana and Specialized bibs and I prefer the Giordana. The bibs are absolutely critical on a tandem since there is very little opportunity (compared to a single) to change position. BTW, good luck in the Chico Velo. I'm sure you'll do fine.