The Science museum had a nice display in Chicago of U-505. They cut holes in the side, and opened some of the hatches to allow easy access through part of the boat and out the side further down. The sub was partially inside the building. Access was easy and the sub still had enough original interior that visitors could enjoy the experience. Not perfect from a purists point of view, but the display always had long line ups.
I believe some changes have been made since I was there last, so I don't know what it is like now.
On the other hand, when I visited the museum at liverpool, I had to prearrange a tour, pay extra and squeeze through the sub. (I'm a pretty big boy) I enjoyed it, but access wasn't anywhere near as convenient as the sub in Chicago.
Glad it's going to be preserved.
Darren