I had an exterminator friend tell me that mice enjoy chewing spray foam, so only use the kind with fiberglass in it. Not sure which brands, but not regular Great Stuff.
You might want to consider laying a piece of 1/2" vinyl board along the floor and nailing it into the plate. Not sure if it comes in 1/2" but you could rip some 8' 1x's into 1/2" strips. Waterproof and quite chew resistant.

Steam is water vapor; water vapor is not steam. A square is a rectangle; a rectangle is not a square. Both are parallelagrams; but a parallelagram isn't a square or a rectangle. A thumb is a finger but a finger is not a thumb. Things are just like that sometimes.

This. You can't really see steam itself. All that white stuff is water vapor. Look closely at a kettle with boiling water. As the mist comes out of the spout, there should be a clear space at the opening, that's the steam. It quickly condenses into water vapor, which is what you see. Don't stick your finger in it.

There was a case in New Jersey where a black bear chose to winter in a small garage built into the side of a hill. When it was discovered, the authorities suggested it be left alone so as not harm it. The garage wasn't used for a car, just storage, so no big deal.
I've also read that bears do NOT reuse their dens for at least several years. And they typically don't use dens made by other bears.

Look for a small reflector; 4"-6". With a Dobsonian mount. (Up/down and sideways.) They grab enough light to see neat things, but are easy to carry and set up. Most will come with a 20mm -22mm eyepiece. That's a great wide angle, low magnification choice. Maybe you'll want a 10mm-12mm or something to get closer looks of the moon, but I prefer the lower power ones for nebulae and clusters.
I think Sky and Telescope had a 4-1/2" beginner scope that was nice. Look at Telescopes.com and see what they have. Try a local astronomy club. They love to share and someone might even have one to sell.
And a good finder scope. I like the TelRad but the Rigel is nice. (You can ignore this if you can make the one that comes with the scope work.)
Then find a decent book for small telescopes. I like "Turn Left at Orion", but there are others. These will help you actually find nebula, star clusters, etc. rather than just trying to find stuff.
Go to astronomy web sites and see what they say. Figure a few hundred dollars at least for the whole thing.
You can store them in the garage or shed. Keep it covered so dust and mice don't get in it and it'll last for years.