Just a quick addition to Lazy's answer. A folding stove will, in all likelihood, leak, the trick is, if your flue (chimney) is good, it won't really matter.
Once your stove heats up, it will start drawing air up the flue creating a draft. This will cause the body of the stove to be at a lower pressure than the surrounding air, meaning any leaks, will just become spots to draw airflow.
The only issue I can see with an unsealed stove, would be that it will be difficult to get the fire banked, but banking a fire in a small portable stove is always going to be difficult.
Note: bring a co detector with spare batteries, and make sure you get a good vertical chimney going. If you have a low vent to the side, it will never draft properly, and wind can force smoke into the tent.