Have yet to use a dry rub on Geoduck, although it should help to retain some of their moisture.
Here's the one we use on our Geoduck's.....
Smoking Geoduck Clams.
Clean the clams.
Brine for 3-5 minutes in 40° brine. (Add 1.0 lb of salt to 1 gallon of water. This makes 40 degrees brine).
Drain and pat dry. Dip in oil. Drain.
Preheat smokehouse to 100° F (38° C) and dry the clams without smoke for 30 minutes.
Increase temperature to 180° F (82° C) and apply a heavy smoke for 30 minutes.
I love Geoducks even better than Razor Clams, (easier to clean the sand off.)
This beats "Canned" Smoked Geoduck, Hands Down!