Choosing Full Bridge Gate Driver
Usage of IGBT's at 12V looks strange - there are very cheap MOSFETs that can drive hundreds of Amps and still have a very low RDSon.
At rates like 4Hz bootstrap, the driver might be insufficient - an external isolated low-power PSU would power the high side transistors for as long as you want. A transformer drive is not a thing there due to the enormous inductance needed at such low frequencies.
For powering high-side switches one can use a simple NE555 charge pump or any other boost converter.