If you pack carefully when camping, you will probably be close on your weight ratings but should be able to stay under them.
Your issue with putting your ATV in the box will be your Rear Axle Weight Rating (RAWR). A good WD hitch will shift up to a couple hundred pounds to the front axle of the TV and back onto the trailer axles, however your ATV will be 600+ lbs directly on your rear axle. You will likely be over your RAWR and it will be up to you to decide how comfortable you are with that and how far you will be travelling.
Tongue weight can vary considerably depending on what you put in the front pass-through on the BH trailers or whether you put heavier stuff under rear bunk and the TW scale will help you make packing adjustments in the driveway and still make sure sure the TW will be in the 12-13% range.
For unserviced camping, I carry a couple of blue hard plastic 6 gallon water Jerry cans that have short spouts that make is super easy to pour into our 84 gallon fresh water tank. 12 gallons will give you 12 navy showers or 3 scrape the camping dirt off kids outdoor showers.