OK. So I added the hollow tower instead, and this is a rare case when a bug actually made the mod better. It turned out the new tower was even more suitable than the one I had intended in the first place. Now, I have the entrance to the interior of the hollow tower up on the wall, while I still have a Load Door from the fort court yard from where I can link an interior. This is great. The player can now go straight up to the top of the highest tower in Primby and have a view, without going through an interior cell first. Good stuff. I like it when a bug inspires good solutions. Bethesda still needs to fix it though. Here are some screenies of the new fort. Tomorrow, I do the interior of the tower.