don't use a Gator, try to find one of those Polaris Rangers. They're built higher and already have a roll bar to secure your armor plating too. Aswell if your going for the "Half track" look. The Roll cage is around the two seats in the front where the cargo space in the back is open, so you could weld on a couple bars and use some tarping and cover it.
The problem with the Gator is that there is no real solid body for you to build off of. Aslo because the box has a lift on it, you'd have to build the for and after parts seperate.
My Uncle bought one of each for the Golf Course he recently built ((White Tail Golf Course out in Eganville)). He'd told me that the Ranger out performned the Gator in ever respect save for the Gator had more pulling power. The Gator is also more prone to getting bogged down in the mud because its so low. He also told me that the Ranger was cheaper to buy then the Gator and was better on fuel.