c240,
Washing can be a problem for sure and you have been given some real good advice so far and perhaps the only tips I could add are use the two bucket method where one 5 gal. bucket is your wash and suds bucket and the other is filled with just clear water and is used for rinsing only.
So you would dip your sponge or wash mitt in the suds bucket and wash one half of the roof. Rinse your sponge or wash mitt in the rinse bucket, rinse off that half of the roof and then place it in your suds bucket to draw more soap. Continue like this all around the car, doing only one panel at a time, rinsing and sudsing.
You may need to change your car soap also. I prefer Pinnacles Car Shampoo as I feel it is very lubricating to the paint. Also, try washing with a FLOW of water just to the front of your wash mitt or sponge. I do this for real dirty cars and it helps out a great deal.
I would though recommend an electric leaf blower for water removal over a wet/dry vac blower attachment but that is my personal preference. As already noted a MF towel is the way to go for drying and using the BLOT technique along with a QD and you should notice the washing lines reduced a great deal.
I have a soft water tank for my business and it works great and I will soon hook up what they call a DI (dionized water) tank to it and I am told this is a true "spotless" rinse. We'll see.
Anthony