I would glue it but cannot tell you how to make it easier. I have minimal experience doing this and it was in tight quarters so difficult in that regard. I imagine you know that many times when dry-fitting, the pieces will not fit together well or completely. Sometimes cannot be separated for re-fit. They need the glue to act as a lubricant. Also, there are sometimes stresses on in-ground pipe that can work to pull unglued joints apart. Without knowing all your particulars, can't predict your particular dangers. I'd find a way to learn to glue.

Have you heard of Aeratis?

Hi, @Mittens Cat! I know it has been a few years since your install, but I would love to hear how you are liking the PVC Schluter--whether it has met your expectations for durability, colorfastness, etc. Similar situation here -- I generallly run from PVC anything, but in our case the softer white of the PVC options is a better color match to our tile than any of the aluminum whites. I thought we were making good progress with tile selection and then I got thrown into Schluter/bullnose/edging world. Two steps forward, one step back :) . Thanks in advance if you're able to share an update!

I looked into Bauwerk windows a while ago but eventually went with a different supplier. One thing I found helpful was checking local companies with solid reviews. If you're based in the UK, www.hadleighglass.co.uk has a good range of uPVC windows and doors, and they offer custom sizes too. Their customer service was responsive when I had questions, which made the whole process smoother.