forums.interwavestudios.com
It seems offline right now, or down, but Interwave has a Nuclear Dawn section with a Community Content section most people post in, they also have a upload/download system for finished maps or something.
As for the prop, not sure if I'm following, but your saying have a submarine prop say on the surface, then you can climb down through a ladder that's in the hull, then go into a part of the map you made that's not actually inside the prop? I don't think so. You should be able to fairly easily make a submarine or other hull type from blocks and the vertex tool. And how much is "Very destructible"
I think my maps blow from a destruction perspective, and the majority of them are fully destructible except for a frame that I use so that if pieces of the floor/wall are floating, it doesn't seem weird since the frame of the building is intact. I think a 95% destructible map isn't enough, how much are you planning
Bragging ftw
P.S.- I can give you the .vmf of my destruction sandbox if you want to look at how it's setup, and it's what I use as a baseline for all my maps with destruction since it's very well tuned and has tons of hours of testing to find the optimum settings; assuming you have destructible walls and stuff