Has anyone glasses the insides first when building a strip kayak?

Should work fine. If you think about it, stitch and glue builders do it all the time. I'm not sure what you would gain doing so.

You could conceivably even make female (external) forms and strip it from the inside. The ends might be a bit interesting to strip though...

If you want to strip it from the outside (with internal forms like usual) I would also cut a few external forms (cradles) to lay the hull into. Say every other one. Strip the hull, pull it from the strong back, mount the cradles on the SB, flip the hull into the cradles and then remove the forms.