I am not sure what you mean when you say
Meaning to treat it like an additive?
Yes it is an additive. 50% Erythritol will not fully dissolve in vg (it will not dissolve in pg at all) make a 5% Erythritol vg solution (5% Erythritol 95% vg) then use it as if you would a flavour or sweetener. In the % range i mentioned before if using with stevia if using solo you will have to use in at a greater % than you would normal sweetener and it will not be anywhere near as sweet.
If you managed to dissolve 50% what you have is not Erythritol.
What do you mean by
Will test it out with the mix of Sucralose for the next test.
Stevia is not Sucralose they are different but both are sweeteners.