i carry straight rock salt in twp plastic bins with latching covers. the bins measure approx 30"l x 18"w x 20" h (35 gal?). they hold about 900lbs of salt together when full and fit behind the wheel well on each side of the bed. i also built a wood frame to box in the containers so they don't slide around. works mint! the latching covers are great as they keep out the snow and water.
On our F-250's we use 900 lbs of tube sand from Home Depot. They are sealed pretty well in heavy plastic tubes so they stay dry and don't freeze.
The manual from Fisher said to be sure to use the ballast or the antilock brakes wouldn't work right. I've been thinking of switching to some 1/2" plate steel, bolted down, so that we don't have to remove the ballast between plowings when we have to load up the truck.
Walt, I'm wondering why you cut the 55 gal barrels in half. The ones I have, both plastic and steel, have full removable tops with lock rings. I use them to store Magic Salt after I've mixed it. Fifty five gallons is right at 660#.
**** these barrels had juice concentrate in them. There is no lid on them just bung holes lol. So i chainsawed them in half so i had better visibility and covered all them with one piece of rubber roofing.