No, not a real UFO, but if someone were to look at it from the ground that is what it would appear to be.  The usual design for a UFO is an ultralight helium craft, either made with all black balloons for night, or a large reflective helium filled milar saucer shapped ballon for daytime.  With enough helium you can lift about anything, which will be enough to mount remote controlled fans on your craft so you can stear your ship, or you could attatch a fishing line to it and fly it like a kite.  For the night craft, since you can not see the black balloons, you cover it in misterious lights that can be seen from the ground.
I'm flying my first UFO balloon tonight, but may soon expiriment with other ways to get the device in the air like remote controlled airplaines and helecopters.  I think balloons are deffinitly the easyest way for now.

Does anyone else have other ideas for an alien space craft, or opinions on this?

I feel this is good performance art that can be very inspiring for people.  As long as it is done in a believable way.

On the other hand it could be possible to use UFO hoaxes as a psychological warfare tactic to scare and subvert the enemy.