Hello Pixguy,
The tube sand bags will rot and break on you at the worst time, been there, done that.
Buying sand in bulk and having a pile of it in your garage to fill the spreader will work and shoveling off the floor into the pendulum spreader with a flat shovel is simpler as you can fill it from the ground as it will lower right to the ground.
In your situation a pendulum spreader will work best and cause the fewest problems because they will not clog
up.
Sand has to be physically moved like rock salt.
You need to look at the smallest three point hitch Vicon Pendulum/wig wag spreaders as they will break up and throw sand clumps with its agitator.
It uses the Power Take Off to operate the spreader agitator through a gear box that swings the spreader tube from side to side to reduce waste and overlap. once you set the spreading width your done period and there is no waste.
The hand controls for the chute to open and close it are directly in front of the spreader while you are sitting on the seat of the mule and easy to reach.
The biggest advantage for you is that it has a heavy injection molded hopper or a fiberglass hopper in the case for the larger ones that will not rust out and it can be filled from the ground with a shovel or a pail.
They are easy to clean with hot water or cold water.
The other thing is if you purchase a truck load of concrete sand that will cost you much less money per pound and
you can use windshield washer fluid to keep the sand flowing and reduce caking and freezing of any sand or salt or salt and sand mixture.
By shoveling or pouring in the sand from the ground level then pouring a gallon of WWF on top of a full hopper of sand will keep it flowing and as I said the Vicon spreader is much easier to use and clean if needed.
I am not trying to spend your money, I see what you have to deal with and the smallest pendulum spreader is the best way to do it simply because its simple to use, has one moving part which rotates and swings the discharge tube in one motion in a narrow or wide arc and the hopper is designed to let the agitator fully empty it through to the ground.
IN a pinch/bad ice layer you can use a gallon of cheap chlorine bleach to mix up with the sand in the Vicon pendulum spreader to melt ice too so keep that in mind to.
Do you have loaded tires and rear chains for your mule?