Prepare the smoker, using wood chips, so that it maintains a temperature of 150 to 160 degrees F. Place the trout fillets onto the smoking racks skin-side down, separating them by at least 1/4 inch and put into the smoker. Adjust the heat as needed and cook until the fish is opaque, has darkened in color and has the desired level of smoke flavor, 5 to 7 minutes. Remove the skin and bones, flake into large pieces, and place in a bowl.
Cut the bottoms off of the creamers so they will sit flat, and scoop out the center flesh of each one.
Whisk together the mayonnaise, mustard, vinegar, dill, horseradish and onions in a small bowl and season with salt and pepper. Pour some of the dressing over the trout, gently mixing to combine. Add more horseradish and mustard, to taste.
Fry the potatoes in batches until they are golden and crispy, 4 to 5 minutes. Drain on a paper-towel-lined sheet tray and season with salt. Stuff the potatoes with the trout salad, and garnish with dill sprigs and trout roe.