We buy cheap protective bits of carpet at motorhome shows to save the vans original carpets. These scraps never fit and if you cut most of them, you can end up with rough bits of fly away raggy edges. I experimented today by cutting the back of the carpet with a metal cutting disc, which gave a perfect edge. Then using latex (copydex should do the same) to paint the edges carefully, I then tapped the edges just before it set. The results are not as good as whipped edges but they are still visually serviceable.