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I have a 15x24 that I use a Cylinder stove in and had the same problem. Two years ago at the sportsmans show I bought a wood pellet feeder attachment that they make for it. When we used it this year I used the wood to get the tent warm before bed, all the corners and equipment and then used the wood pellets through the night, it kept the chill off and burned all night long. In the morning we stoked up the wood to get it toasty in the tent again but the pellets kept the chill off and kept me from having to restoke the fire in the middle of the night. A 3/4 of a bag of pellets lasted all night and they are cheap and clean. I would recommend them as a good option.
Cutting the wood to fill the stove is a great tip. Another easy one for first thing in the morning is a simple Presto log.The pellet feeder I got was very easy to install, they give you a template to cut the hole and it hangs off the back of the stove. I used a drill and a jigsaw, took me about 15 minutes to modify my stove. It comes with a cover plate to put back over the hole if you don't have the feeder with you. You can burn pellets or close the chute on the feeder and burn wood in the main stove. At one point I had the pellet feeder going along with the wood last year. They also have an attachment that lets you burn diesel, kerosene or used motor oil. I went with the pellets because they were easier for me to pack to where I hunt. You can also buy the stove and the pellet feeder or oil drip as a package already fabbed up if you are not mechanically inclined or don't already have a stove that can be modified.
A couple manufacturers make gravity feeders designed for their own stoves, but the most commonly advertised is Cylinder Stoves brand.