You can use a small diameter pulley as well. It helps support the sides and somewhat prevents flattening. Place the pulley in a vice with the tube pulled against the nut. If you can fill the tube with dry beach sand and plug the ends it will reduce the crushing. Heating a little with a propane torch helps.
Or you could check ebay for a 3/8" tube bender and do a good job. I've collected from 1/4" to 5/8' over the years for very little money.
But I agree, that a set of used tubes is the cheapest and easiest solution.
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