Best way I found is through dipping
Get a round rod the size tube you want, let's call it 1/8 for explaining purpose ok, don't get stuck on the size, the real size will be up to you but it will be small.
Next get your plastic of choice, since they are small I would think you could get away with a medium
Plastisol, normal tubes are usually harder plastic made for salt water
Got your plastic all heated ready to use and Dip to about 1" key cool for a few seconds and dip again same size. Let cool and remove tube from rod, cut to size and the split tails by hand using scissors, razor blades xacto blade etc.
There you have a nice crappie tube, the reason for two dips is simple, if you want two color tubes like a red head with yellow tail the you dip the yello first the dip the red only half way
You will have to figure out your self a good way to many at a time but that is best left to his you like to work
Hope this helps homie