Need to get shot

So I towed the trailer into the mountains last weekend with the bike on the lift. The wind was blowing and the trailer towed terrible. Especially going down hill the trailer would push the truck around making for a very stressful drive. Anyway we got out there and it was really nice to have the bike along. My intentions were to have my wife tow the trailer home and I was going to ride the bike to avoid another stressful drive going back home, but .... I wore the back tire off the bike and decided I would feel more comfortable driving an unstable truck back then riding a motorcycle back with a tire that looked like it could pop any second.

Well the drive back was very nice. Little wind and the truck felt much more stable. I got thinking about why there was such a profound difference between the way the 5ver towed going out vs coming back. I think the wind was responsible for some of the unstableness but what may have made the biggest difference is the fact that we used about 40 gallons of water over the weekend. That 40 gallons was moved as we used it from the fresh tank to the black and grey tanks. The fresh tank is over the front trailer axle the black and grey water is stored about 4 feet ahead of the fresh water. I think moving that 40 gallons forward 4 feet shifted about 100 lbs from the trailer axles to the trailer pin.

So in the future i would like to have a few sacks of shot positioned in the bedroom or poured into the kingpin hitch on the trailer to add some ballast to the pin weight.

I weighed the truck and trailer on the way home:

front truck axle .......4960 lbs
rear truck axle ........5440 lbs
trailer axles ..........14440 lbs

Tare weight of truck rear axle is 3480 lbs.

Any ideas on where to get a cheap couple hundred pounds of shot.