How thick was the layer that you removed? One thing you could do is to cut anything from a piece of 24 lb. paper to a piece of 110 lb. cardstock so that it covered the area on the inside of the tube and trim it so that it just fits without overlapping itself. Then use a craft stick, a piece of scrap wood or a stiff piece of cardboard to spread a thin layer of white glue or wood glue onto the patch and immediately apply it to the inside of the tube where you peeled off the layer. Then take a dowel (the larger in diameter, the better) or a length of PVC pipe and insert it through your tube and use it to "roll" your tube back and forth on a smooth flat surface to press the paper down evenly all around the inner wall of the tube. Use whatever thickness of paper that will fit and while maintaining the clearance for your payload section. If you end up making it slightly too thick (so that the payload section won't quite fit or fits too tightly), don't panic. Once the glue has thoroughly cured (overnight or longer) you can lightly sand the inside until you have adjusted the fit.
White glue is the adhesive of choice for something like this, but you might want to consider using a good brand of wood glue (Titebond II or III or Gorilla Wood glue) for it. It might add even more stiffness as well as being more sandable.
If you want to use epoxy, use it with patch material (such as the paper) rather than by itself. And use laminating epoxy (aka "finish cure"); this type of job is what that epoxy is formulated for. Not only will it bond the patch well, it will also soak into the paper and stiffen it.
Finally, one other option is to use drywall tape (the open fiberglass mesh type) with laminating epoxy, applied to either the inside or the outside of the tube in the area of weakness/thinning. But don't use spackle with it; instead use epoxy. You will be able to sand it smooth. You can even use the mesh in combination with one of the other methods, , by putting down a layer of the mesh and then covering it with a layer of paper, for example. It may take some effort to fill the mesh (that's when topping it with a layer of thin paper may help) but it's a cheap glassing method.
MarkII
