We fill it up on the site that needs it. Usually we break it up since we usually have a pallet left in the garage all summer long but it still gets stuck and the controler beeps like its out of salt. My dad wants the viberator but he doesnt know if its worth the money or he should just have me or my brother in the back feeding it in.
I had that happen once with the same spreader. What I have done since is when I know there will be salt in there for a while while plowing, we will spread a tiny bit once in awhile to move the belt and keep it from settling & freezing on the belt. I've left salt in there many times between storms and never had problems, but it seems like wet salt will have a problem especially if the truck is plowing. I think this is because the constant stopping & starting and vibration of the operating truck caused the salt to settle & compact itself in the hopper, then freeze. Haven't had a problem since now that we keep that belt moving through the night to keep it from compacting too much.
I believe the unit you are talking about is a single stage spreader. You really want to use nice dry, non clumped salt in those types of spreaders. A vibrator will help it perform better, but its probably not going to break up those big clumps, and they will always get stuck in there. You may also want to get a screen for the top of the spreader so that when you're loading you can easily filter out the chunks that aren't going to work.