Looks very neat, hope that this solution works for you.
Sorry to say I disagree with the last two posts. If the material was rigid I'd agree, but it's not, it's very flexible. You appear to be in a 'between the devil and the deep blue sea' situation. If the rivets are placed too far apart you may suffer from pull through, if they are too close it may result, due to flexing, in splits between the rivet holes.
I would find it preferable to have pull through than splits, with pull through you have a second chance, but with splits it's more or less finito. As you have learned, a split can only be repaired by welding, which of course will leave scars, and the welded seam will not be as stable as the original material. Not only that, think of the extra cost, plus have you experience in welding plastic, it's not so easy.

One other small point, I would leave the reflective tape off for a while. This way you can check the riveting at regular intervals, then when you're sure that all is well replace the tape.
With all the hard work you've put into this project I hope that all goes well for you, I'll keep my fingers crossed for you.
