Hello everyone.  I have been teaching myself Solidworks 2017 for use at work for a few months, so simple snags are still pretty frustrating for me.  I would greatly appreciate your advice and suggestions!  I am using the flex feature to create a tube.  I have chosen this method because the tube will be lined with extrusions, and the best way I know to do this is to create the flat plate first, pattern fill with my extrusions, and then roll it up with the flex feature. 

The problem is when I use the flex feature- weird things happen depending on whether the plate's edges meet or overlap.  If the edges meet one another precisely, I don't understand the result, but it looks like an empty outline of the cylinder I am trying to create.  If I overlap the edges, only the overlapping section of the tube remains.  If I do not overlap the edges, the entire tube remains, but this is not acceptable because I need a solid tube.  I have tried moving the trim planes in both directions, but the issue is still not resolvable for me. 

Can someone explain what is happening?  Even if there are suggestions for a better method to achieve my desired geometry, I still would like to understand this issue with the flex.  For my help request purposes, I am attaching screenshots and files that include only the tube with the flex feature- I'm omitting the extrusions that will be lining the tube.  I would be ever so grateful for your help, and I will pay it forward in the future when I am more competent with Solidworks.