Rail boats aren't good for CZ's because CZ ships are too tanky. I also did try long range superpen and it did work for module sniping though, whenever I hit them. But ammo was too limited to consistently win anything other than 1 low CZ with them, mostly because I kept missing. I had better luck with long range plasma slug but it's still just a lot slower than beams + multicanons.
You also need good convergence, likely a limited ammount of rails for heat management and a thermal spread low emissions power plant.
The ship I do bounty hunting in for BGS though is a 4 Rails Krait Phantom and it works wonders and one of my favorite things to fly, I think that's what you should try. I don't worry about module sniping, I just go short range blaster + plasma slug. 4 of them on a Phantom and you'll chew through anything in a haz-res. Try not to ram anyone, since your power will run very low and you won't have amazing shields because of it.
I occasionally take it into low intensity CZ's and it works well too, just not as well as the usual beams + multis, there's a reason those are the PvE meta.
Alternatively you could do it in a Krait Mk2 though it's less agile and agility is key for railguns since the way you're supposed to kill ships with them is by just hitting shot after shot affter shot repeatedly. You can fit 5 rails in them and you can avoid overheating by having 3-2 in the fire group instead of all 5 on 1 button.
Thanks for the advice. re the Krait though, seems an awful waste of those large hardpoints.