Y'all might want to try lower wattage bulbs. Unless this is in a 40s F basement, you are really very unlikely to need that wattage. I'm currently running a 175w about 18" above the litter in a 2.5x3' topless brooder, in a basement that is 52 F. (Only 10 chicks in there but the pool of warmth would be big enough for 25+)
There are three advantages to a lower wattage bulb. 1) less chance of fire (from melting the tub or any other method). 2) lower electric bills. And 3) creates a smaller 'pool' of heat, which in a smallish brooder you kind of *need* so that there can be too-warm and too-cool areas to let the chicks regulate their temperature by where they hang out.
You can get floodlight bulbs at 100, 125 and 175w, either red or clear if you look at enough stores; they work perfectly well as brooder lamps.
Good luck, have fun,
Pat