I made my front box out of treated wood. Bottom - 1/2" plywood. Sides 1X6" board. Attached with deck screws. Did not drill holes in bottom because they would fill up with crap anyway. Any water in box - detach box from ATV and dump out. Make sure your handle bar head light has free movement.
Cut out a piece of carpet for the underside of box - nap side up to eliminate any unnecessary rubbing or squeak.
Make sure the box width will hold 2 - white 5 gallon buckets (paint and plaster come in them - pretty handy for tools and such) or 2 - 5 gallon Coleman Model 5620 spouted water jugs.
A single chain saw (Stihl Farm Boss or Stihl 32)with fuel and oil containers will fit, plus splitting mall, wedges and cant hook.
I have even carried 1 - 2 day old black angus calves in the front box.
As far as dimensions, I followed the basic shape of the steel front ATV rack and made sure the buckets and jugs would fit. Two tight bungee cords and your good to go.
Portable waterproof container on rear was purchased from local Farm and Fleet store for $25. Drilled a hole on each side and bolted a plastic electric fence insulator on for the bungee strap to go over.
Nothing permanent about this set up. In 20 seconds it is all stripped off.
Oh and one side note - do not paint the boxes BLUE if'n you ever expect to get close to a deer.
Front view of box with models to show case it.