Sealing a circular seam in plastic, and driving myself insane

[CharlesHouse]

I am building a large prop hammer from a PVC inner frame, two coroplast end caps, and fabric around them. The end caps will protrude from the fabric maybe 6" and be visible.

I built the rough end caps today, cutting a circle in coroplast with four joints that bend over and attach with long strips around them, little a huge bottle cap.

http://www.therpf.com/attachment.php?attachmentid=421059&d=1420227760

http://i.imgur.com/411jToH.jpg

http://i.imgur.com/SQJar17.jpg

The issue is covering where the circular piece and strip meets. There is a gap that I want to cover. I could cover it with tape, but the prop is purely aesthetic, so I want it to look good. I could paint it after, but then I would simply have consistently colored tape. If I use something like putty or clay, it will crack when the coroplast gets bent or shifts slightly. Basically, covering a circular seem is making me feel insane. Any ideas?

 

[division 6]

Epoxy putty like Aves, Magic Sculpt, Plumbers Putty.

 

[Scotophor]

Rework it so the circle fits inside the rim, then attach them by gluing a bunch of "L" brackets on the inside. Use a flexible adhesive like silicone caulking.