I know a lot of you are going to hate this, but I found an easy way to make just about any size tube
mod.
Take the tube and cut to size. Sand the edges.
Take the tube, spray it with cooking oil, stand it on end.
Place carto metal tube inside new plastic tube.
Fill space between plastic tube and metal tube with non-toxic hot glue. About 1" deep should be fine.
Cool, then push glue mold out of plastic tube.
With the metal tube still inside glue mold, cut mold in half with sharp knife.
Cut off ends of mold for a clean edge.
Now you have the top and bottom seal for your tube.
I'm testing a couple to see how it holds up.
I'm not terribly worried about the hot glue, as it's safely used in aquarium applications. I'm not sure if the vg or pg will react negatively with it though.