you can reduce, or completely take away, all the power needed to lift it by making it bouyant.  if you make a tank out of carbon fiber, you can make a tank that is light and strong.  fill it up with hellium, and it will float.  have a computer add in presurized air or no air by a fan

And how big an envelope will this thing have? I mean, it'd be the size of the Good YearBlimp. Literally, for similar reasons - which either has you driving around with an unamoured gas bag or a huge issue trying to protect it.

Fail :)

 Cross country mobility is the major drawback of the hovercraft - they can't clear large ditches or scale long slopes or tackle sharp inclines. Add to that the requirement to maintain a high power to weight ratio just to even work and you've got something that's expensive, thirsty, lightly armed and incapable of tackling anything other than fairly flat terrain.

Ian