here is a thought for you, a sportsman incubator has a 200-225 watt heating element. theoretically one heat lamp will be sufficient. to much heat is a bad thing, i knew a guy who tried to replace a heating element with an oven heating element, he ended up cooking his top layer of eggs, the bottom eggs never got close to hatching.
the heat should be gentle, and not blowing directly on the eggs.
i will see what i can do on a paint drawing on how to build an incubator the size you're looking for. how many eggs are you trying to hatch at one time? do you want to incubate several weeks worth of eggs at a time with a seperate hatcher?