Low propane indicator?

If you don’t want to step outside, get a cheap endoscope camera for your smartphone or tablet and mount it in the propane compartment facing the regulator. You still won’t know when it switched over but could at least see that it did. I’ve never used one so I can’t comment on the ease or quality. In theory, run the cable into the RV and just plug in when you want to check it.

Also once you learn about how much you are using you should be able to approximate when you’ll need more. If you’re really burining through it in a day or two, consider a larger external tank as was suggested above.