Have Caribou cases (Pelican) with Hepco Becker racks. Ugly but I really like them. Slid down gravel roads with them, multiple tip overs in all sorts of conditions. A bit scraped up but never lost their waterproof integrety. Buddies with metal cases seem to have them deformed easily and loose their waterproofing.
Once got too close to a concrete wall and whacked one of the bags. The lock is designed to be the weak point and allows the bag to be knocked off. Carry an extra lock - takes 5 minutes to fix. This points out the only negative thing in my mind which is they are a bit wide.
- RexBuck's Latin America
Information on travelling in Latin America.
Includes links to ride reports to Mexico and to South America