It's not really a problem, at least I'm pretty sure I'm doing SOMETHING wrong but I don't know what.
Whenever I make a Cube Dropper instance, even if I copy/paste the stuff from the Wiki, when I save and reload the map it refuses to appear, all it appears as is a tiny purple box.

Have you tried validation portal 2 authoring tools? That's what I do when that happens.

Arachnaphob wrote:
Have you tried validation portal 2 authoring tools? That's what I do when that happens.

Tried that, it still doesn't appear :/

is your map under sdk_content/maps ?
Is the instance under sdk_content/maps/instances ?

TheTobbell wrote:
is your map under sdk_content/maps ?
Is the instance under sdk_content/maps/instances ?

A: Probably not, I'll check ^+^''
B: Yup

They don't have to be in sdk_content/maps per se, as long as the instance VMFs are in the same folder as the map. (Or one or more subfolders.)
So if you keep your maps in a different location, just copy the instances folder over there and select the dropper VMF from that copy.