Julie
I keep my car outside like you. It is washed regularly using a SnowFoam, then a Good Shampoo and then on a monthly basis I use a Hydrophobic water solution to spray the car, before finally drying and buffing . It keeps very well, dirt does not stick and washes away easily . Any rain or elements in the air form large bubbles and run off the car. I do also always use a pressure washer, nothing fancy, just a cheap Karcher model.
Best Wishes, John