I've got two concerns though.
Firstly I wouldn't be happy not having a water tight barrier between the tank and the bulb bases. I think condensation is likely to form on the metal parts when the lamps are off and the fitting cold. This could lead to disaster when the lamps are switched on again. I built a similar project last year and think the use of household power compacts is great but thought must be given to the fact that they are not designed for aquarium use.
Secondly, though you may have no trouble at all, is the fact it's made of plastic and them bulbs are gunna get pretty hot. Time will tell.
Good project & good luck