I think the most important thing to consider is just how "mobile" mobile is. Sure you can pull a Vandread and lug a coffin with you, but then you have a coffin that can surely be whittled away it in less than an hour to get to your defenseless body. So while a coffin on the move is possible due to the unstated RAW, where it is when you go back to it is vital. Just how many places can you trust to see your wispy form go flying by and not capitalize on the opportunityto kill or imprison you? So while mechanically this sounds like a great advantage (I'll move my coffin every four days between seven castles), who can you trust with your life to do this?
Additionally, almost every D&D campaign I've been in has taken some liberties on the more classical lore. Your DM (assuming you're not it) might have different ideas as to just what a vampire's weaknesses and abilities should be.
Yes, you can.
As stated in the spell Gaseous Form:
The creature is subject to the effects of wind, and it can’t enter water or other liquid.
Emphasis Mine, size doesn't matter in a gaseous form, as you will be subject to the effects of wind as any other gas would be
In addition to the effects noted, a gust of wind can do anything that a sudden blast of wind would be expected to do. It can create a stinging spray of sand or dust, fan a large fire, overturn delicate awnings or hangings, heel over a small boat, and blow gases or vapors to the edge of its range.
With Rules as Written, you can definitely cast Gust of Wind as a standard action, then using your move action to move into the gust, to carry you along.
If I was GM though, I would rule against this use, as the spell to me seems intended that a single blast of wind comes from the caster, moving away. The actual ability of the caster to get caught in the gust seems very ambiguous. It's your game though, and if you feel that the Vampire would be best served as a storyline villain, and not just a once off, that's something to discuss with the table. Just make sure you don't have anyone ready to snipe him off after the 60 ft. that he moves.
Best Answer
Vampire spawn assume gaseous form at 0 hp like a vampire does
The vampire spawn (Monster Manual 253–4) possesses the extraordinary ability fast healing that, in part, says
Thus, despite its fast healing functioning at a slower rate than a full-on vampire's (2 for the vampire spawn versus 5 for the vampire), the effects of either being reduced to 0 hp remain largely identical, and that includes a vampire spawn assuming gaseous form.