I've used a Low Watt Density, and now use an Ultra Low Watt Density element. Neither scorch my bags, full blast with grain holding the bag against the elements. In fact I've touched my LWD element once, with my finger, and could hold it for half a second or so. Not bad!
I use voile fabric that I get from the fabric store, and have also used sheer curtains, just a big single panel sheer. The fabric store voile works better, nicer weave and better sized.