Answer: The plant may be suffering from shock due to the switch to dry indoor air and lower light levels. Unfortunately I do not think the portable greenhouse will work very well in that it would be prohibitively expensive to keep it warm enough during the colder parts of the winter, it would also need to be automatically vented to avoid overheating on sunny days.
You have basically two choices about how to keep it over the winter. One is to try to keep it actively growing, to do this you need the brightest possible location (a heated sunroom or conservatory is ideal) and would treat it like a normal houseplant keeping it at normal room temperature to a minimum cool room temperature of about 50 degrees. A pebble tray or humidifier can be helpful in keeping the air moist enough for it.
The other method is to let it rest and hope it can come back in the spring. To do this, keep it cooler and on the dry side just short of drying out completely. Temperatures of about 45 would be good, some people find that a garage or cool cellar works well. It does not have to be bright because it is so cool and the plant should go dormant. In spring, bring it back into the light and begin to water and fertilize it again.
Either way, you will want to trim it back either now or in the early spring to stimulate the next bloom cycle as well has help keep it a manageable size. Be sure to gradually acclimate it to the outdoors again next spring once the weather has settled. Good luck with your shrub!
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