Heating any greenhouse any way is expensive. I don't heat mine, and I find insulation (bubblewrap and polystyrene sheets) keep out the frost. Depends really on what you want to grow. I would certainly not consider heating a greenhouse on the lottie. No power, so no leccy heating possible, and with gas and paraffin you have the potential fire risk (that's without the vandals getting in and causing further problems). I use my greenhouse to overwinter perennials (just frost free), to grow on seedlings in the spring, and to grow tomatoes, peppers and chillies in the summer.