Hey there!

Is it possible to create an activator without a model which the player could activate? Would I need to create a custom model for it to work?

Create a trigger, select new as the type, give a name to the activator (under ID), edit your trigger reference, go to primive tab, and select "player activation". If you don't see the "activate message" in game, rotate the trigger by 90°.

Cheers! Works perfectly!