I use a tractor battery to start my pressure washer and a Deep cell Marine Battery for my reels and Fat Boy Pump. I have to use a charger for my marine battery. Can I use the Marine battery for everything. I'm not sure if I can use the marine battery to start the pressure washer. I don't want to ruin the starter or charging system.
If I were you Art, I would get a cranking/deep cycle and save a little space. And depending on how much you run your PW, and how many amps your engine is putting out,.. you may not even have to charge the battery anymore. My Honda GX630 puts out 17 amps. But there are some that only put out 3 amps.
My trailer is always hooked to my van. I have a little 12v hand truck sprayer, and I wired into my cigarette lighter and ran it back to the trailer, so when I'm driving it keeps it charged all the time, and I never have to manually charge it. Not sure if something like that would work in your situation or not. You could actually utilize both the PW engine and the 12v wiring from your truck.