Hello Good Dr.,
Have you ever smoked a turducken? or tried one? Can you recommend a rub for one.
I've never cooked a Turducken myself, it's just a little too confusing for my way of cooking. But I've eaten a few so I know a little bit about them. For the readers who don't know, it's a boneless whole chicken inside a boneless whole duck inside a boneless whole turkey! And in between the birds is typically a well seasoned stuffing made with rice. It will take a long time to cook, like 12 hours long. Most of the folks that make them supply you with their preferred method of cooking and I'd suggest following that. Of course you should be able to convert their method to your smoker without much problem because cooking something that big will always be done at a fairly low cooking temp.
As for a rub, well the birds are going to be well-seasoned from the inside because of the stuffing so it won't need much. It's also going to cook a long time so I wouldn't use anything with sugar or chili powder or paprika, so I think I'd use salt, pepper, and a little onion and garlic powder and that would be all.