Single spring foothold traps in the 1 to 1.5 size work well too. On rat and weasel sized creatures hey act like a body gripper. Just look up a foothold box setup for weasels and that'll do the trick if you have any long spring footholds available. 110 body grippers work well too. Both of these you aim for the rat to walk through the trap and they get caught. With a standard rat tra, try setting the trap in a box that's tge same width as the trap, just tall enough for the arm to clear the top. And the only opening on the side of the trigger. But have the hole just big enough for the rat to get in, about 1.5" diameter should do it. Then put the bait behind the entire trap in the back of the box, make the bait a big chunk of something that they will try to drag back out the hole, so if they make it past the trigger one direction, the effort of dragging the bait makes it much more likely to get caught. This is the weasel box set up, you can guard the opening with any of the traps I mebtioned. This way the bait isn't drawing attention to the trap and the rat will walk right ontop of it, hitting the pan. In this setup a large pan works best. The 5 gallon bucket method will work too. Just remember that rats are used to and good at swimming. So you can always add something to the water to lower the suface tension so that they have more difficulty floating and it takes more effort to swim.
Kyle