I have a box truck and a small trailer for backup. We are pretty diversified in that we offer a broad range of residential services. Mostly Roof cleaning, deck staining, driveway sealing and house washing. We need space to haul several pails of deck stain, pails of aggregate sealer, chemical tanks, water tank, hoses, pails of dry chemical, surface cleaners, wands, electric sprayers and pump sprayers. This is a lot of stuff and it all has to fit, be organized and still have room to get in and out of the truck. If the truck breaks down for any reason I am down unless I have a back up or I do the repairs myself through the night. Which I have done many times. We always get the job done on time even if I have to rent equipment.
If you have a box truck you need to protect it from all the water and chemicals that you will be subjecting it to. If not you will be tearing it down once a year to restore damages cause from the water and chemicals. If water and chems leak onto your frame or tail lights, etc. you will have problems. It is easier to dispose of a trailer and get another one than it is to dispose of a box truck.
Box trucks are great, but you need to address these issues if you don't want costly down time or aggravation. Also, a box truck does have maintenance needed to tighten framing and rivets, etc.