It's interesting that you use Testers glue to attach the leather. It does make sense as you describe it. I used to carve leather back in hippy days and always used rubber cement for most attachments unless they needed stitching or riveting for strength. This would remain more flexible that dried model glue, but probably is not a critical factor anyway in a model. Seems it would stick to plastic fine, though the melted glue from the Testers must sure give a good bond.
I'm also surprised you can get skins that are so thin. I always skived mine down when needed, but having them already done is pretty nice. Gonna have to do some hunting around. Nothing looks as good as real leather.