Thanks for the comments all.
Here is what I did...
Once the seedling is doing well and ready for a repot, you need to find a pot with drainage holes ONLY IN THE CENTER NOT THE SIDES.
The reason for this is that -as you know - it puts out long underground suckers. Sometimes they come out sideways but sometimes they go straight down. There does not seem to be a limit to how long they grow (within reason). They keep extending until they find light then they start to open into leaves. If you have holes in the sides at the bottom of the pot, that's the first place they will come out. We don't want this, we want all the growth at the surface. Besides a pot with a center drainage hole, you also need to get one with a rounded inner edge at the bottom so when the runners reach it, they don't spiral around and around but just go straight back up to the surface without stopping. So what you are looking for is a wide shallow bowl with a hole in the center.
I used a mix without stones so the runners did not find it too difficult finding their way through. Bark, charcoal, polystyrene, perlite for a nice spongy long lasting mix. I don't use sphag or any other type of moss in the mix any more. Nothing but trouble. Then top off with some finer bark or something. I kept in in the shade house all year. This winter was cold! regularly got down to 3C, sometimes 0C but average about 5-7. I don't think it's that important. 10C would be fine.
After reading Tanaka's advice I never let them dry out. Perhaps a little less in winter but never dry. A bright spot where they get good winter light and plenty of fresh air movement. In summer, plenty of water every day. I sprinkle lime (crushed shells or whatever) every few months. It's seems hard to overdo it. Feeding is standard but they don't need very much. Flower buds developed in late summer/autumn and just sat there doing nothing until late winter when they slowly started to extend. I think the cool ''rest'' stimulated this cycle. I suspect that moving them when they are spiking is asking for trouble.
Paphluvr. Yes it's a bonsai pot but it's hanging up where there is more light and air. (and no mice or rats)