Well, as most tents arent insulated, heat retention will always be a problem. And a lot of them do have quite a bit of mesh, because theyre most often used in the summer when ventilation is the bigger challenge. The Eureka! Headquarters ($360), for instance, is big enough to sleep six, but has mostly mesh doors.
Plus, 10x18 is a huge tent. Theyre really not that common. I think your best bet will be to get a canvas outfitter tent. These tend to hold heat better than a light nylon-and-mesh tent and have fewer (if any) windows and mesh panels. Take a look at Cabela's Outfitter Wall Tent in the 12X17 size ($800). Its a real palace with lots of room for double beds, duffels, clothing, gee-tars, and more. Its very sturdy and weatherproof, as well. As a bonus, you even could add a Cabelas Tundra Takedown Stove for use inside the tent (its equipped to take such a stove). The stove is $230. How cozy would that be?
Of course, this isnt a tent you take backpacking. It weighs 80 pounds, and the stove would add another 40. Plus, do take care with storage. Its canvas, so if stored damp it can mildew like a champ, even with its mildew-resistant treatment. Dry it thoroughly after use, and store it loosely where it can ventilate well.
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