Hello Dave,
I have a lot of young seedlings too,such as EH,TH,EP.I will stop watering complete.Because the temperature is too low.I hope your seedlings can safely spend this winter.
Best regards from China
Qiyanwei
Thank you Qiyanwei 
Hi Dave,
if your seedlings are 1 cm or more in diameter, you can keep them dry and cold during winter. If they are smaller, it's better to keep them warm with additional light, or to keep them dry and cold for a shorter period (e.g. till January), and then starting growth in a warmer place with additional light and moderately increasing humidity. Watch for spider mites during the dry periode.
Put a toothpick to the ground of the substrate, take it out after about 10 minutes, and then look, if the substrate is totally dry.
Hello Ernst, Thank you for the reply. Some are more than 1cm and some are less then 1cm. I have a growbox with lights so I will put the smaller ones in there for the colder months along with the new sowings for this year. Thank you again for the help 
regards
Dave
Hello Dave,
my seedlings stay all the time in the glasshouse (also 5-6 C) and no water the whole time in winter just as the big cactis. Some seedlings have only a sice about 0,5 cm and I have no wastes. I wish you much success in breeding for your seedlings.
Regards
Jürgen
Thank you Jürgen also very good information to know
best wishes
Dave