It’s also helpful to provide the rats with a lot of free lunches. No water under the perlite for a while. When they regularly frequent a site for the grapes and nuts you leave for them, they’re not only comfortable with the setting, they trust the bait and maybe they let their guard down. Maybe. :(
The current bucket trap I use has an aerosol can with an axle from the nozzle straight down to the bottom that makes it a rolling cylinder. This is mounted horizontally right below the rim with a ramp leading to it. You smear some peanut butter on it and they will walk out on it and then it rolls. It has worked well.