Hey TAZTG!
Hot glue, by itself, would not likely hold the panel for a long period of time if you were just to put the hot glue down and them put the window on top of it. Hot glue excells with oddly shaped surfaces, not perfectly flat and smooth surfaces.

*buuuuut*

If you were to drill a small hole where you were putting the glue, and then put the glue on the back of the panel, then push the window *with the hole* over the glue (so that the glue pushes through the hole and adheres, that may make it a stronger joint.

Typically, I use double sided "super tape" for my window mounts. Is is a 3M tape... I'll get you the model on that stuff. Would recommend that more than hot glue. Super strong, and damn near permanent.