Ways to make a flimsy plastic case more sturdy?

[Jan Pospisil]

Per the title - my Portable PCIII keyboard has lovely white alps, but the case itself is quite flimsy. It has three screws at the top edge, but only plastic clamps at the bottom. And it flexes a ton in the lower half. (both top and bottom case halves)

As I didn't find anyone mentioning anything of the sort, I suppose drilling through the case and tightening it with a screw+nut combo (maybe with an additional metal plate) is not something that'd work?
I saw people mention putting standoffs inside, that might be doable. (at least for the flex)

[PlacaFromHell]

You can fill some parts of the keyboard with epoxy putty, always being sure it will still close, but be aware that this may affect the sound. Also you can put some long metal pieces in between. If you can upload some pictures of the insides of the case I would glady advise you as better as I can.

[Jan Pospisil]

OK, I'll take pictures next time I'll be taking it apart.

[Findecanor]

Gluing on any rigid material onto the interior of the walls to thicken them should work, as long as it fits.
I've seen people do that.