My setup of GRUP is more of a policy rather than something special.

I keep with the conviction that the bootloader is the most important
piece of software after UEFI/EFI/BIOS. The reason is because a
bootloader is what loads an OS without which a user is at a loss.

To achieve the above, I keep a small, 1GB, partition reserved for a
very minimal installation of Debian/Devuan that is just the base
system with many utilities missing. This small base system is achieved
by installing using debootstrap. The latter, installs the base
packages but no accounts or network connections are setup. To this
small base system, I add a root account, configure
/etc/network/interfaces to get network access, configure /etc/fstab,
and finally, install the flavour of GRUB that is pertinent to my
hardware and os-prober. At the end, I boot this minimal installation
and run update-grub to get a skeletal version of grub.cfg. To be safe,
I make a copy of this grub.cfg. At the end, I manually edit grub.cfg
to display its menu the way I want it.

With grub.cfg caution must be taken to follow the syntax precisely as
GRUB's developers do not absolutely expect anyone to manually edit
that file. Make sure you understand the syntax structure and keep a
working copy of grub.cfg open so that you can consult it to follow its
syntax. Make sure a '{' has a corresponding '}'. Also be aware of the
use of non-printing characters that may be needed. In other words, you
have to be cautious like a real hacker.

So that you can follow, I am attaching my version of grub.cfg. I am
editing the UUIDs for security reasons.

Note also that I am using this setup on a GPT formatted disk. For an
MSDOS FAT formatted disk you have to use msdos instead of gpt. Consult
the outputted grub.cfg when you first run it. Furthermore, I am using
this setup to boot MS Windows 8.1 using chainloading.

PS:
If you dedicate more space, you can use a distribution that is known
is capable of installing a base system and use that to install your
version of GRUB. That way you will end up with a bootable installation
that you would use to manage GRUB. By keeping that installation only
for GRUB management you will guarantee yourself that your machine will
always boot. Please, be aware you will need to not install GRUB in any
other installation. Be also aware that this is an unorthodox method of
managing a bootloader but in my experience it worked very reliably.