If i were you i would go with the cooltube.Dont worry about the ballest temp.Your intake will be fine then just put a little fan in the cab for circulation.Maybe a desk fan right next to the ballest to blow heat in the right direction and you could play it off as just a desk fan for the room.The cooltube will be great for you 250 isn't that big of a light at all so you need to max your lumen uptake use mylar and drop your light to about 8-10 in if possible with that cooltube be sure not to burn.Hey maybe an extra intake with a exhaust reversed to suck air in.A little one out of a pc tower works good for lil cabs good luck