Weight on a tractor will help traction.
Weight low to the ground helps to stabilize the tractor - lower is better, both from side rollovers, and keeping the weighted end down.
So, fluid in tires is very popular because it is very low, really stablizes the machine, and is out of the way. Note that antifreeze solutions are lighter than water, while real tire liquids are heavier than water, doing a better job.
Rear wheel weights are nice because you can remove the weights easily when you don't want the weight. But the center of gravity is slightly higher than with fluid.
A rear weight box is mostly only for conter-balancing a loader. In addition to the weight keeping the rear end down, it also acts like a teeter-totter with the rear axle as fulcrum and takes some weight of the front axle. They are popular because you can build them many different ways, add or decrease weight as needed if it's a box, build in storage for tools, chains, shovels, and so on.
Some people just use their heaviest 3-point implement as a rear weight and this woks ok, but for me I work in very tight locations and I would not want to be banging up my walls & fences, as well as the implement.
In your case you might want the stability of some fluid (you can go 50% intsead of a full load of 75% fluid) plus get a rear weight box for when the loader is on.
Since my computer locked up while typing this message the first time, I will post it on both your messages. /forums/images/graemlins/smile.gif
--->Paul