I always appreciate the less-plastics approach and applaud your determination to do your part. I make my own yougurt and store it in glass jars for the same reason. My daughter reuses the gallon jugs to start all her seeds in winter.

A few questions I can think of -
Do you sterilize the bottle and the distilled water? Depending on bottling/handling methods, Dr Joe Falkinham and his students have found that distilled water is not always sterile.
Where do you store the homemade solution, and for how long? My daughters (RN's) taught me - open sterile containers at room temperature are to be discarded after 24 hours, refrigerated after 72 hours. Knowing that bacteria don't reproduce well in 7% saline, I personally would fell safe storing in the refrigerator for up to 7 days.

And a caution - be sure when pouring the sterile water into the nebulizer not to touch the lip of the bottle with fingers.

If I need to return to daily 7% saline nebs, I will definitely consider this!