Heavily salt your fish; you can even bury them in salt. I use kosher or sea salt for this. Put them in the fridge for 1 hour per pound of the pieces of fish, i.e., if it's a 2-pound piece, two hours, a half-pound piece, 30 minutes.
Briefly rinse the fish and pat it dry. Let it sit on a rack in a cool place for at least 1 hour and up to overnight in the fridge. At room temperature, put a fan on the fish to speed drying and to keep bugs away.
Get your smoker to a steady, cool temperature. I use a Traeger, so I set it at 175°F or even 165°F. You can't really do this well if you can't keep your smoker below 200°F. Wood choice is yours, but for a Mexican flavor use mesquite. Alder, maple or apple are other great options.
Smoke the fish for at least 2 hours, and up to 6. The lower the temperature, the longer you can smoke it for. Four hours at 175°F is a nice compromise. Serve the smoked fish hot right away, or let it cool and use it for other dishes.