When I cut the lower hull off of a ship model, I glue on a flat piece of styrene so the hull is stronger, and it will slide along on the wargame table easier.
These 1/72nd scale models are about three feet long. When only doing the upper hull, there are not too many parts on the kit.
I taped the hull bottoms to the hull sides to help hold them in place while the glue is drying.
The late war versions of this submarine had a snorkel, it allowed the submarine to cruise underwater and stay hidden from Allied attacks.
Once the glue is dried, I have to trim the edges of the hull bottom flush with the sides. My long term plan calls for two of these submarines, and one early war Type VII C submarine. And maybe some others...