Hi Sharif, is the attached model what you're trying to get? I found a little easier method using booleans instead of trim.

What I did to start with was make this tube all filled to start with, no wall thickness yet:




Now boolean union those 2 solids and that has the outer skin how it should be. You can now clear the inside of one direction by selecting the combined solid and using boolean difference with the inner curve as the cutting object.

To clear the inside in the other direction, extrude out the inner curve here a ways past the juncture and use that extrusion as the cutting object in boolean difference:



- Michael