The worst part is the trunk for the hybrid is even smaller than the trunk for the other models (EX, LX, etc.). That's because the batteries sit right behind, and up against, the rear seat. If memory serves, the cubic feet available on the hybrid is 10.3 (and the EX is 12.something). It's not very big. Roof rack or the other thing from etrailer.com sounds like your best bet.

Support the Troops - Drive a Hybrid!