Clumpy Compost

We raise goats and rabbits and produce lots of manure for compost. The rabbit manure is easy to handle, but am having trouble with the goat barn manure/straw material making big hard clumps (or soggy, depending on the weather.). We live in the southern Great Plains where rain is either sporadic or a deluge. We have been composting in large simple piles. Would it help to cover the piles in plastic, etc. or to use some type of tumbler? Husband is a welder and can fabricate whatever might be needed.

Can you use chickens to turn it? http://geofflawton.com/videos/chicken-tractor-steroids/

I would not cover closely with plastic the pile needs air for the proper bacteria , turn more often if you need it to break down quicker , you can also layer with branches to help provide air spaces and pull the branches free to help aerate
if you have a loader just flip the pile more often pallet forks also aerate the pile great ( Iused to do this by hand , bad back makes this some thing I can no longer do by hand )