I am an expert with more than 15 years of experience in the field of embedded systems, electronics, prototyping and PCB layout. I have worked alot on bootloaders for several MCUs including USB MCUs like PIC16F/18F, AVRs and STM32.
For PIC18F, I have the hardware and PICKIT3 with CCS C and MPLABx to provide you a working code.
Regards
Ch