How can I secure my paper towel roll turrets to the base?

When I made my castle cake, I had the paper towel rolls covered in fondant, I piped Royal icing around the inside edge on the bottom, I also poked toothpicks through the side were it would attach to the "castle wall" and also used royal icing were it would touch the wall. They were pretty sturdy with the combination. The ones on the second tier I also attached toothpicks to the bottom of the paper towel roll with royal icing to help anchor them. They were a little less sturdy and next time I think I would attach them after transportation or use longer dowels or skewers because there was some "wobble"