To those of you in the north that drive pickups. How much weight do y'all put into your bed to help with traction? I bought 300 pounds of sand bags this year, and it doesn't seem to be helping at all! Last year I used two of those concrete parking stops that my dad had laying around, but i didn't like the fact that they took up pretty much my whole bed. I have no idea what they weighed, but they actually helped. So I'm just lookin for how much more weight I need to add?