I run long rakes of wagons, using Kadee's to couple them, but rather than weight the wagons out of the box, I cut a 1.5mm square of black paper, and insert it over the end of the axle into the axlebox, spiking it onto the axle before re-inserting it. This provides a very cheap way of adding a small amount of resistance. If the wagon is still too free-wheeling I put a paper square on the second axle of the wagon.
Hope this helps as its very cheap and easy to do
Chris