The trick is to leave them long enough in decent amount of smoke while warming. I never go over 2 hours before getting them to 165*. I take mine straight from the fridge to smoker. (the outside is already dry enough) This gives me time to add smoke and warm them up before grilling and still well within the 140 in 4 rule.
When I dump a fresh hot chimney in sfb to sear the steaks, I leave the brats in the smoke chamber. At that time they are usually around 150* IT.
After I sear my steaks, I close the sfb lid and when the brats quickly rise to 165*, I move them to sfb grill and just roll them once across.
Skin snaps with every bite, and juice will appear on your chin. LOL
It's funny,
but I quit doing brats on my grill (didn't have my smoker then) 20+ years ago. They were either burnt, or too tough and dry to enjoy, or underdone and then more cooking was needed, and that dried them out too.
I just recently took the plunge again with CG offset smoker, and the texture, smoke flavor, and juiciness blew both my and my wife's mind.
We love them now.
Don't give up. Just fine tune your method.