Not only a flat bed, but a bail bed.  Yes it does cheapen the insurance a huge amount.  We use our bail beds for just about everything.  Not only for hay, but picking up everything from four wheelers to parts on the ground.  Dad does not own a hoof anymore, but uses the bail bed just as much.  Personally we like Krogman beds from Sabetha Kansas.  Little cheaper and have the arms on top so stuff does not slide off.  They can work with ya on a size and make what you want.  Not as bulky or heavy as a DewEzze, and comparable to a Triple C, which is also a good bed. 

With what you are doing with your truck, balebed to me is an obvious choice.