Outside is no problem. Key to avoiding water spots with the newer coatings is to avoid sprinklers or any type of municipal water spray without drying. Normal rain water won't be much of an issue unless you have a tendency to leave it dry in the sun.
There are a number of good options but I'll keep it simple and tell you Cquartz UK 3.0 with Cquartz Gliss v2 over top of it. It's my go-to coating system for customers and it lives on my Son's car that sits outside and on mine which is garaged most of the time. You won't have any issues. My additional tip is to use their Essence polish. It's a base-coat SiO2 layer / primer, plus it has some fillers that get sealed in thus why they call it a gloss enhancer. It's very good. It also helps with removal of the coating, although UK is pretty darn simple and easy to use.
Hope that helps.