I've got a recipe book for smoking fish (The Kiwi Smoker, by Carl Scott). It's just a little paper back booklet, but full of neat ideas. Here's what he suggests for trout and salmon:

Brine:
3 litres water
1/2 cup white sugar
1/2 cup pickling salt
1/2 onion, sliced
4 cloves garlic, crushed
1 tsp dried basil
1 tsp bay leaves

Immerse the fish in the brine for 5-6 hours and refridgerate. (If this amount isn't enough to completely cover the fish, then increase proportionally)
Remove the fish from the brine, rinse, and pat dry. Place in the fridge for another 6-12 hours.

Then, smoke your fish (time depends upon size of the fish, temperature, what kind of smoker you have, etc).

I've not actually tried this yet, but it would be worth a go if I can think to prepare the fish the day before!

- Jeff