Another suggestion beyond John T. (post #3), is to be sure there is enough clearance once you are at the point of inserting the tube. This is a combo of drill size and any sanding done prior to painting. I do not paint the tube, as it is unnecessary if the painting process for the hole is good and remains intact. There are 2 more things I do as part of my process. Right after painting the hole, Run the tube in and out a couple of times to clear any clumps, etc. Also, I will smooth the outer edge of the end of the tube with sandpaper. This allows a smoother entry for the tube, less likely to scrape some of the paint away.
Many others have gotten a handle on this, and are able to use very translucent tubes...you will too! There are some VERY nice blanks available to you once you master this process. With the suggestions here, you can be nicely encouraged...go get 'em!