If they had a verbal agreement with the last tenant,   and the last tenant gave notice or has officially abandoned per definition thereof  (you can look for things like them having cancelled their utility accounts, emptied unit of their belongings, etc)  then they can't prove anything and maybe you can use that approach.   

Can I simply give them a 30 day notice to evacuate my house or does the pandemic affect this as well?

He has my tenants number for giving them notices on coming by.

Unemployment numbers are decreasing.

And from my experience with appraisers, they wouldn't notice the crawl space, and even if they did, they wouldn't know what they're looking at.

Can he end the lease early if he gives 60 days notice, or is the landlord able to make him pay through all 12 months?

I’m curious, has anyone else noticed an increased in inventory of Multifamily properties?

As for your comment regarding duplexes in CO, we noticed that as well in SLC.

Then next day they reported a leak in the garage, their story was that they noticed it the day they moved.

If you have a team on the ground in the area, you have one of them put a code box in a nondescript spot so it is not noticeable.