Hi from Jim!
This android app will let you check the seats remaining for a given trimester and CRN.
Using the menu on the upper-right, you can store a series of CRN's to use as reminders of your courses. The button on the lower right quits the app.
If it doesn't install directly, it will be in your download directory. Click it there.
You may have to allow install of this app from an "unknown source" because it didn't come from Google Play.
Download app here