Start with the microchip one (PIC32-UBL), pull out all the stuff you don't need and hook it to your eeprom access routines.
There is no margin in reinventing the wheel here, and the UBL does at least mostly work.
Note that getting debugging to still work with the relocated main program (The boot loader will probably NOT quite fit in the boot flash) requires a certain amount of pain in getting the linker script right, but it can be done.