Any largish hardware store has better. Find the 55 gallon can liners, the heavy duty 5mil ones, and they usually have them in a dark greyish-green. Slit the bottom out of one, and curl up to retain heat. Or, slit two, join them with duct tape, and stretch out.
That being said, tube tents really do suck. As much as I loath a conventional, single wall lean to, they still might be better than a tube tent. Carry a poncho and a small mesh hammock, and get the sleeping bag mods made your liner, it works at least as well.
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-IronRaven
When a man dare not speak without malice for fear of giving insult, that is when truth starts to die. Truth is the truest freedom.