The nursery is in the business of selling plants. ;o) I grow some 200 woody plants in containers, some as bonsai, most as potential bonsai. It is very difficult to grow temperate deciduous plants indoors, though some expert growers have been able to do it. The obstacles you will face are:
) Low light levels will produce weak and succulent growth on this full-sun loving plant, so watch closely for insects. Even in a sun room, light levels are about equivalent to shade or dappled shade outdoors. This will cause the plant to operate at reduced vitality levels and under stress.
) The plant will want plenty of good air circulation. This helps keep pathogens and insects at bay and strengthens stems.
) Actual root temperatures should remain south of 90*, the temperature at which you should start to see a dramatic decrease in root function - try to maximize air flow and keep the pot shaded.
) This plant will not live w/o a dormant period in winter. I suspect it will require somewhere between 1200-1800 hours of chilling at temperatures between 32 - 45* F.
) This is a genetically vigorous plant. Most are not grown on their own roots (grafted) and are very prone to basal and root suckering, which is exacerbated by the continual pruning that will be required if you are successful at growing the plant, so expect to be doing root work during the growing season and a root-prune/repot every other year, at a minimum.
) Foliage is coarse.

I realize this sounds very negative. I'm sorry about that, but it will be a challenging plant in a container.
Did you say you like Japanese maples? ;o)

Al

Yeah - what Al said :-)) I was trying to think of a tactful way to respond to this inquiry and couldn't come up with anything more that this is not a good idea and could very well produce a very short lifespan for a very cool (and typically valuable) plant.

Lack of air conditioning in a glass enclosed sunroom in Missouri could produce some pretty uncomfortable temperatures in summer - perhaps too warm for anything not considered a tropical. Lack of heating in winter may not be a problem but enclosure and insufficient air circulation and low humidity very well could be.

This is a pretty hardy plant, grows to an impressively large size and makes a stunning winter focal point - any reason why you can't plant outdoors in a suitable location?