Living in a truck is conducive of bathing techniques that require small amounts of water. I CLEAN UP DAILY ON A HALF A GALLON. I stay just as clean as a ten minute shower.
Have your chlorine and your soap or detergent handy, pour a couple drops into your container along with whatever soap or detergent your using, this keeps things nice and sanitary. Dip in your rag, and go to it, when done, your cleaned up. Throw water out, and your basically clean enough to attend a mobster wedding bash.
You don’t need lots of water to clean yourselves up. I only use 3 gallons a week to wash, a little deodorant is a good thing, except if your hunting or hiding.
Start this process now so it is not a big shock later, water is precious, start learning to conserve now.