USB-Serial DFU to nRF52840 on nRF91 DK Board

[OryF]

Hello, thank you for taking time to review this.

I am trying to setup a serial DFU setup for the nRF52 on the nRF91 DK board. I am running into problems getting it to work and understanding it in general.
I looked at several pages trying to help myself understand it
1) https://docs.zephyrproject.org/1.12.0/samples/subsys/usb/dfu/README.html
2) https://docs.zephyrproject.org/1.13.0/devices/dts/flash_partitions.html
3) https://mcuboot.com/mcuboot/readme-zephyr.html
4) https://docs.zephyrproject.org/1.12.0/samples/subsys/mgmt/mcumgr/smp_svr/README.html
5) https://github.com/apache/mynewt-mcumgr-cli
    As well as the links on these pages

I have tried several processes, but for the sake of conversation I will explain my most recent approach.

I compiled the MCUbootloader:
-in mcuboot/boot/zephyr/build

1) cmake -GNinja -DBOARD=nrf52840_pca10090 ..
2) ninja
3) ninja flash

Once I have flashed the bootloader
-in /zephyr/samples/bluetooth/beacon/build
1) cmake -GNinja -DBOARD=nrf52840_pca10090 ..
2) ninja
3) ~/<path/to/source>/ncs/mcuboot/scripts/imgtool.py sign \
--key ~/<path/to/source>/ncs/mcuboot/root-rsa-2048.pem \
--header-size 0x200 \
--align 8 \
--version 1.0 \
--slot-size 0x69000 --pad-header \
./zephyr/zephyr.hex b_signed.hex

After both are completed:
-in above build dir
1) nrfjprog --program b_signed.hex

Error:
Parsing hex file.
Reading flash area to program to guarantee it is erased.
ERROR: The area to write is not erased.

Notes:
I have tried signing the bootloader and loading at 0xC000
I have tried adding CONFIG_BOOTLOADER_MCUBOOT=y to the beacon prj.conf

I am just having trouble putting this all together and understanding how it all works and how to do it. My goal is to load some project like bluetooth/beacon, then use a serial DFU to change the project image to like the hello_world example and have it load into slot1, then switch it to slot0 after verification and then load hellow_world on reset/boot.

Thanks for your help

[OryF]

UPDATE

So I moved to just using cmake and noticed in the Makefile a menuconfig option existed. So I explored that and saw I could specify the offset I wanted the image to be loaded at here. I could do the same for the bootloader. I set the bootloader to not verify the image on boot (just to simplify for now) and then flashed it, an of course it prints
        ***** Booting Zephyr OS v1.13.99-ncs2 *****
on boot. I then configured the offset on the hello_world image for slot0_partition. When I have CONFIG_BOOTLOADER_MCUBOOT enabled it acts like only the bootloader image exists, and prints the same thing. If I disable CONFIG_BOOTLOADER_MCUBOOT then it prints out my custom bootloader message and my example image. This makes me think that maybe I am uploading the image and the bootloader to the offset which would explain why it doesn't change its boot behavior when CONFIG_BOOTLOADER_MCUBOOT is enabled, because slot0 would have the new bootloader image and the application image in it. I could obviously be wrong. I also tried uploading signed both ways and got the same results as the unsigned method. I am still just trying to pass in an original image, have it execute that, then once that works pass in an image to slot1 and have it swap to that.