Sounds like you are on the right track. I have a friend who rooted quite a few grape vines and was quite successful. He would also scrape a strip or two of the bark down to the cambium between the nodes that were going into the soil to encourage roots to form there also.

The other difference is that he would usually get his cuttings in the fall and do it then, putting them in cold, but above freezing storage for the winter, then bring the cuttings out into the light and warmth in the spring. By staying around 45 degrees during the winter, it would give a good chance for roots to form without having the above ground buds trying to draw moisture and nutrients out of the cutting. Light wasn't necessary during the cold period, just when they came out to start the roots growing.

Walter, I have heard muscadine dormant cuttings are very hard to root. They are usuallly propagated by air layering. I would consider trying to graft some of them to increase your odds of success. For rooting I would put bottom heat on them - heat the dirt but not the top part. Put a thermometer in and get the sand to about 80F (I don't know the exact temp for muscadines, thats just a guess).

Scott

Good advice from Scott, but I would add that using very strong rooting hormone is also very helpful, if not essential. Dip-in-grow at near full strength sometimes works. Most of the hormone powders are way too weak.

If you have another muscadine vine established, then saving some wood for grafting later is a good idea, since the odds of successful rooting is low. Wait until mid to late spring when the new green shoots have reached the same diameter as the cuttings, then graft a one or two bud piece using a simple cleft graft. Wrapping with parafilm is best, but strips of saranwrap will work. The wood on muscadines is really thin, so the simple cleft graft is really the only practical way to do it, other than T-budding later in summer. Once the graft takes off, the new growth can be layered or used for rooting green cuttings.

I tried rooting some muscadine cuttings last year, and only had one out of around 20-30 cuttings take. In contrast, for grape vines, all I have to do is stick them in a deep pot, two nodes deep, and they root.
Are the cuttings you're trying to root dormant or in an active growing phase?
Lon Rombough, in his book "The Grape Grower", describes a muscadine rooting technique of taking green cuttings from a vigorous growing shoot on a vine. They are taken early, no later than bloom time. Cuttings are around 6" long with 2-3 nodes. Only the top leaf is left attached, (leafless cuttings don't root) and it is cut in half to reduce transpiration. Cuttings are dipped in a rooting hormone, planted in a mixture of three parts perlite and one part peat, in a mist bench with bottom heat. If a mist bench isn't available, they can be misted by hand several times a day. The cuttings are placed in a bright shady area- no full sun
He advises against using a plastic covering, but says the cuttings can also be placed in a black one gallon pot, bottom heat, and covered with a plastic bag propped up with sticks, as long as the bag doesn't touch the leaves. If you scroll halfway down the page of the link below, you will see this described in great detail, with pictures.
Our local hydroponics store sells rockwool cubes for rooting difficult cuttings, and I've had varied results with those, using other kinds of cuttings.
Kiwinut's suggestion of grafting a few of the cuttings on established vines and layering the vines later is a great one.
Good luck with it.

Here is a link that might be useful: Green (softwood) cuttings