you don't have to remove the gas tank. however, you will have to cut the front-ride cylinder bracket that the airbox is anchored to so that you can reuse it after removing the covers. you'll see what i mean when you actually get in there.
These covers are a composite insulating plastic that serve as heat shields to prevent your knees getting toasted. Other than that, they have no functional purpose, unlike the plastic cover above the drive pulley that directs air flow behind the hot exhaust area of the rear cylinder.