All Splawns have a serial loop. I had a SmartGate a long time ago. If you intend to keep that pedal then just put it where you have the most hiss as Smash is saying. If you don't mind ditching that pedal for something that will do both front and loop at the same time, then get something like a Boss NS-2 or an ISP G string Decimator. Those have the capability to do both at the same time.
If I had too much hiss coming from the amp, I would try to eliminate it. Like a bad preamp tube or bad power feed. If I had too much hiss on the front end, I'd be looking at my guitar, pickups (height mainly), proximity to amp, cables, pedals, etc that all hit the front end. I hate hiss.
My Quick Rod is super quiet, even without a gate, but I use a NS-2 so it is covering my front end of the Splawn and the Recto and the loop of the Splawn. Recto is still a hissy bitch no matter what