You can use just about any container for minerals as long as it will keep them dry. I have some that are made to hang on a fence or board, and some that are just homemade troughs.
Try to put them high enough so the goats wont step in them.
Keep them filled all the time and the goats will eat what they need.
Loose minerals work better than blocks. They are easier on their teeth. I've never used the ones in a bucket so I dont know their consistancy
Its also probably best to use metal or plastic. I have used wooden ones before, and if they arent kept full, they will often chew the wood. I've had sheep eat completely through the middle of a 1 X 8 wooden trough