Use the expanding foam with caution. Some expanding foam will swell and shrink with a change in temperature. If you get it in a can, from the hard ware store, buy the kind that goes around window and door frames. I believe it is more stable.
Also, if you would like to make the layout of the moonbase more accurate, check this site.
http://www.space1999.net/moonbase99/technical_section.htm
Click on the image of the moonbase near the bottom of the page. But, making it more accurate means chucking the vac parts and sculpting your own.
Good luck!