I rate rugging them in the winter, About £15 off ebay..
I think as has been said, A heat lamp in a kennel that size would be too much and she cant move away from the heat source, But i do rate heat lamps aswell, Iv got just a plain open wooden dog box ( Its a raised old whelping box) that iv got in the garage with the heat lamp above it, And everytime one of mines does a shift its stays in the garage under the heat lamp till the morning or night if theyve done daywork, Then rubbed down rugged up and back in the kennel....