Louv's Way: remove bumper, but leave wheels on.
Greg's Way: leave bumper on, but remove wheels.
Your choice.
I just updated my page
www.louv.tv/ducts with a couple of templates for cutting out the air-exit holes in the covers.
Be sure to remove the covers before drilling or cutting into them!
www.louv.tv/ducts/LeftSideDuctHole.jpg
www.louv.tv/ducts/RightSideDuctHole.jpg
These are templates from the Factory duct holes. These holes are larger than they need to be. But that is nothing more than an aesthetic problem.