[Chromebooks] jhedfors:
This is what I do, and it has been working awesome. I have done it several times experimenting.

Starting with a dual boot Windows and Linux Mint setup, each in their own partition, plus another partition which I refer to as "storage" (sda4).

From Linux Mint I have download Sebanc's Brunch package and Rammus Recovery image. I extract them both, and place the recovery image inside of the extracted Brunch folder.

I install the pv, tar and cgpt packages/binaries if they are not installed already:

sudo apt install pv:
sudo apt install cgpt;
sudo apt install tar;

I then run the following from inside the extracted Brunch directory (making my img file 20 gb):

mkdir -p ~/tmpmount;
sudo mount /dev/sda4 ~/tmpmount/;
sudo bash chromeos-install.sh -src chromeos*.bin -dst ~/tmpmount/chromeos.img -s 20;
sudo umount ~/tmpmount;

[IMG="Successfull install"]https://lh3.googleusercontent.com/2xZ6ispodZEJEPJobaRW_5xN9Ga6w4-7KN6QmlO13sVu8zrTkATaL_Sz0tdhaT9GX2dtM_WWnoocXbYTWgFkWw0FyIVKSAtyptPbeQa0bHhuBq6fC1Qyvk_ySOI1ucWVH8sBHbNXWCQcH-0f0nn_oHdc-xDRAKIiecetFH9EKHiYnwrbLwTrlpGSxO_z0zFct72cjE_hz0gQ51cgrwoA73_zl6O6P3KD8kPi7WQYg-r5zXIoyTTJRgLPYRZhTWMaRnvCMi74wGOBupZ5pgTlsV_R97-T8pKIYHiKZOyvDafJFQNno2TzNHWBoQTQsSUzfsJrQGmylJl5-G9WskSXC_pt9XQxvEORvUjotL8ElU21a23q9upqS2aPDrBDgmalaIvue83FjtLRASXP1WNje4b86PwQ9OP7h_FGZS4GBXxq937pR1F1AQmgW7QH1iCXaAlN7vXoRicBSqC1Y5XayRhuC2U1Uq7FKFe1Fp1jczz331WSu2h7A6U_2XlcCvaVi8-VYv4ZPr5NjlnMl0jbxBRhNIpkr7XDVhL34uSZf-LYfarfEESWXvT27GjP-E_8PJp8cnLq85U-vwylDOZQo62AvbcTLBYwqVKz4ZnsWoQ11uJEUd43BRt26hvqHiIrYq5WY8bAg-aG9gVX1koEBqY1qiKyrqdTqNyedqsfbKy3PWaHEzHX4eduKCr6tw=w852-h288-no[/IMG]

[IMG="Success!"]https://lh3.googleusercontent.com/jGxMhr9NctdcDMl4Y9Y_JUhBl7q-T1GEl3A_YTx17QsFwxnES_1R8Bu_wWck8K6hQKgMkKNYjhQ4HZuRfyu6ZY-gXXBhepEPgBvsUGwNnoAbpHV2aJQwhrHzWG6utFLTxMPkg2-vRcrxjAhjlzytsSsGv9qDEv3pbCE0-d-pJsk6NrA7K05z1rbiTalNbfYn9QksT3mXXtbN5aDe-6BZqPu1ai9g2_zcYCjnBKihHizHJ-otlFtqNFeY6IYnkxUitpN1WohIybE1nRQXVE1CHmD3n8E-AUJ0lqldz6HLx0TS4OtCKP3ATEZ6B3sV6wit3iD-zPH9TJ4ylPDCYCLz5Wn8DUfgrUu4eR9E9aRKFYlEsUvnbRQF_V6aFVrB-hh-ViWVZfpDX1UPsei_Ksjmo9Cgv4ckL0Begj_pCVR8Rs3nwPJwj7zQwZx74_HYzaxXDmpKwjqW_2ShE92eoBc-Kq-MpAxaLYl0YJe5su00XwE54YS24J-wRGSr4QuTTRA_ErbALsD00-c5-R32Gzxr6WHbrVAlLGCxbYYNZm6EsstZ-gh9xi-sJkiSif15OARFNyzT25UaZKmXfz8w6T9EsIMNJ2ijjX1OXHT4Tv6gJc1wRRWWJx5_cWWaL8ZBYIxMA3_iGrb61ayByqHxlRS2qXvZmAUr2BiD9oh4PIxgdOG_u9KVlI59yfQDH-tWWQ=w656-h470-no[/IMG]

Still in Linux Mint, I will then add the menu item for launching the image from the Linux Mint grub2 menu.

There are different ways to do this, but I use grub-customizer:

sudo add-apt-repository ppa:danielrichter2007/grub-customizer;
sudo apt update;
sudo apt install grub-customizer;

I add a new menu item, selecting "other" as the type, pasting from what is displayed at the end of the chromeos.img creation):

img_part=/dev/sda4
img_path=/ChromeOS/chromeos.img
search --no-floppy --set=root --file $img_path
loopback loop $img_path
linux (loop,gpt7)/kernel boot=local noresume noswap quiet splash loglevel=7 disablevmx=off \
cros_secure cros_debug loop.max_part=16 img_part=$img_part img_path=$img_path
initrd (loop,gpt7)/initramfs.img

[IMG="grub-customizer"]https://lh3.googleusercontent.com/aHtXzW4jqXvXKH5dBLayqvMZyktUg97BiywuUJvHu-oI4IjRkGZoXtHrhebLnqUKscR0RTJWKvs6X7SUejfUHepEwYszjWdQY6lMFV5g7A2fj4qNZvqh2sLgmN4pFYZAGtKAGoDalvUD7vPr9b8QHv5cKCpM9y1RInWI6d_e41Q1j3-SeXQMNumIXNF8kipfKwwZue_YNbPG_S8r_kPsYMyRUhDCI5cNz_A7imNw1KeyJmPEqUbd5qHV9qM2zpLwU0eOpOxEJLuAiROnah10dmXN9TDUv0_GpMaugX-148Dg3_5onqnXSBoNgAwkWtr5MfttzBWen0qA0lfQZ7BUKlnPr2NIEmmLfir2tK107TRgzXYRGEcva17noU1z2OF4eQK18btWk8Gnkx7S1Zd0tU0ncG2OUo2AIu3grfG8Q6SOalk0EIaJ9WM2M65cSyaGr7E9BI7ENqX-rWGjOgnaTz1kiPJBnLG2oZsu23IsWgtalm84I2NKunTFPZ1RTLP_cTTR2rUTbETwx_Fk8qZQm7rfi3id5pi3CE2QO_U7Isal6-4xvLNIiZ6wSIV7_SbSOBO4jRjWQtKYhGhO5tMPzuybFQS_SorXpBMbnfbpZBctlSDfIJx8e2aw6ez9lb1pNzHTls0UYZ-yEYVvCAtbf7PRjakH77RA1u-T-aj9jbt9WalbODS5qQNuC4SEvw=w900-h548-no[/IMG]

I then reboot, and I will see the Chrome OS option in the grub2 boot menu.

I hope this is helpful to someone. :)