Ive seen feeders similar to what tomsyellowbreeches is describing at several different beagle clubs.
Most of em cut a small plastic barrel in half longways and mount it so that it will help keep the feed dry and also protect the rabbits from flying predators.
Salt blocks are 50 lb blocks of salt that are put in pastures for cattle. Theyre not that expensive, maybe 6 or 7 bucks. You buy one of those then take a hammer and bust it into smaller pieces and scatter it around the property. Ive always heard that rabbits need alot of salt and that it will help them with reproduction, etc.
Ill see if I can find a picture of one but you basically take a 5 gallon bucket and cut a hole in the side of it at the bottom big enough for a rabbit to get into, then put some of the busted up pieces of salt on the inside and put the top back on it.