i prefer heat pads personally. I've heard bulbs tend to dry the air out. I can speak from first hand experience the clips are not at all secure. I have a corn missing right now because of trusting those clips. If your screen top is a metal frame you're alot better off than if its a plastic one (cause the plastic ones flex more in the middle. I would put a clip on each end and in the middle of each side and still put some book or rocks or something on top if its a plastic frame. If its metal i'd say you'd be ok with the clips you have and then the books, but still yet better safe than sorry and clips are cheap .