rs485 bootloader tutorial?

I am hoping someone will be able to help me on this one. I am trying to figure out how to implement programming over 485 using Unos and 485 shields. I have a multi-drop system working well, it's just that I can't easily access the board to update the program (identical program on all boards) without doing it through the 485 system. I have looked at SodaqMoja/optiboot github site (GitHub - SodaqMoja/optiboot: Bootloader for Arduino boards) and he seems to have solved the problem, but I am a noob in the bootloader arena. I believe I have all the software/hardware necessary to make it work (usbtiny, avrdude, avrdudess, atmel studio), but I need someone to help me understand what to do once the bootloader is installed. How exactly do I write the program to all the Unos over the 485 network?
Many thanks for any advice,

I see no indication that the RS485 worked, also no clues about device addressing.

What I ended up using was RS422 to bootload the remote devices. And for addressing I have managers that share their state on an out of band channel.

When a host connects to the serial its manager will share that with the other managers and select a single device (bootload address) to place in a tempory bootload mode (so only the host and the bootload device can talk).

You can look at one of the shields I use, it is complicated but does work.

Well ^5 worked, I am updating it at this time, I finally got the power off (IOFF) buffer working on another board and wanted to add it. Also note, there is no change needed for optiboot or avrdude to make those work, but it is not friendly with the Arduino IDE (which is not really a priority since it is more for a headless Pi).