You looking for just a "backup" type setup, or running in parallel type for more electrical power? I have friends who have done this on older trucks (K5s, etc), they have used isolators successfully. Our F-250 diesel has duals, as do most heavy duty trucks now...it can definitely be done! Just different setups depending on what you want it for...and seeing how your truck already has the extra tray, probably can source the parts from the dealer if you wanted? (Although expect to pay WAY more)
The name of the company is escaping me right now (damn this getting old stuff!), but there are a few well known companies who specialize in this subject...google "dual battery setups" and "isolators" etc, and I'm sure they will come up...they sell complete kits if you want them, or you can put parts together yourself. Also might want to check out some Marine stores, they do this all the time and have really heavy duty isolators and such...