Park The Truck!!!!
Ok now you have to look at operational costs. Hopefully you are not working for small froffit margins. For the winter months can either make or break a wash buisiness here in the north.
What I found is the work becomes so weather dependent (temperature) Even more without a shop. For me even with a heated shop the trucks don't even move if the daytime high doesn't go above 22'F. If you do the crew will spend more time tring to unfreeze things or making ice than washing. Plus the results will suck.
I'm not saying you cant make money in the winter months but the profitablity will steeply decline. I'm not sure of your equipment or mounting style. But your options are truck mounting a winter system in a van, cube van inclosed trailer and use lots of RV antifreeze. Or invest in a heated shop.
Here is the ultimate soution; Wash when the weather is right, temps in the high twentys or up(we seem to have lots of warm ups during the winter months) and invest you summer savings and get into snow plowing/salting for the winter.
Even last year with the mild winter the company was 35% more proffitable in the winter months, even with shorter work weeks.
Good luck
DAFF