Re-re-emphasised, unless your gun is already wired for a mosfet, you'll have to do a bit of soldering. Without a mosftet, the circuit is very simple, with the trigger just acting as a switch.
With a mosfet, the power wires run from the mosfet to the motor, and you'll need to rewire the trigger tabs as signal wires to the mosfet, generally using thinner wiring. It's not complicated, just a few dabs of solder, but there's no avoiding it. And you'll have to open the gearbox to do it, unless you have a V3 where the trigger tabs are accessible from outside.