[RPM] buffing weapons to do damage for a duration

[ericthered]

I am about to play a MH game as a witch, and one of the stunts I want to be able to pull off is buffing a weapon. It appears that the most obvious route, adding a damage modifier and a duration is both illegal and overpowered. So I'm trying to figure out something else.

Is the proper way to do this 'add an innate attack'? either follow through or linked?

For example, making a knife blaze with fire could be built as follows:

Greater Create Energy(6) + Added attributes 2d Burning attack (melee C,1 -20%, linked +10%) (9)+ duration 10 minutes (1) = 48 (16*3)

On the other hand, a hand gun with rof 3 recoil 2, range 200/2000 enchanted especially to destroy undead, but that only works on penetrating their flesh, would look like this:
Lesser Destroy Undead(3) + Added attributes 3d toxic attack (follow up on rapid fire 3 +50% recoil 2 -10% range *20 +40%,only vs. undead -20%) (19)+ duration 10 minutes (1) = 23

Am I building this right? or should I be using bestow a bonus or the damage-duration combination instead? And should I be adding the weapon weights?