Sad to admit, but I rarely washed my car prior to getting my box - I once went about 3-4 years without a wash on my old car. As a result, I had to re-learn how to wash a car.
I don't have a house or a hose and there are no hand-wash places around where I live. As a result, I use DIY car ports. One instant word of caution is do not spray the canvas top with the jet on high intensity. Gently spray on lower setting and start from a distance.
I have determined that DIY car ports are crap for washing a car if you only use the jet. To get junk off that car, you need to hand/bucket wash.
I use them only fo pre-wash rinses and post-wash rinses. I do everything (washing and waxing) by hand.