Mr. Grumpy - The reason for a hovercraft skirt is to provide a flexible seal between the craft and the ground/water surface. If everything was flat and smooth, then a shirtless hovercraft would probably work, as a uniform cushion of air could be maintained. Unfortunately this is not reality. I used to like the concept of a hovercraft and once keen to model one, but having seen real ones and models lack of directional control have gone away from the idea. Another reason for the skirt - bouncing off nearby objects in the vicinity of the hovercraft.
Without a skirt your model will be limited to smooth surfaces such as floors and patios. It may even struggle on grass. However, if you're willing to accept these limitations you'll also bypass one of the tricky components of RC hovercraft!