You can achieve this with either the REL1100 or the OUT1100. I would use the OUT1100 if your SSR can be controlled with 5V.
Changing the PWM duty cycle to 30% is as easy as using setDutyCycle(0.3). See the API tab on the product page for more information.
Changing the PWM frequency is possible if you upgrade to the latest OUT1100 firmware (v.120). To upgrade the firmware, double click on the OUT1100 in the Phidget Control Panel. If your Phidget libraries are up to date, it should give you the option to upgrade. The minimum PWM frequency for these devices is 100Hz, so you won't be able to get down to 50 or 1Hz using this feature. If you really want to switch the output at 1Hz, you can probably just use a timer in software and toggle the output every second using setState.