I get my silk from 'Dharma Trading' and it quite rasonably priced too. I buy 11yd bolts of habotai, either 5 or 7mm, and usually pay about $3.50yd. As Zor has stated you need to use stixit or similar, and usually 2-3 good coats before covering. If needed I then give then give the covering a light misting of clean water to tighten, just enough to dampen but not saturate. The habotai from dharma shrinks both ways, from memory its 8 and 5%. I then usually use a fabric sealer, and then finish with auto acrylics.
I dont think personally that I would go to the trouble of doing a trainer that way, unless its to get the feel of using silk covering specifically