Ok, I've been successful installing Devuan 2 (ascii) under Debian into a dir with the following conf file to be used by the tool "multistrap" (s. Debian repo).
It reports a keyring error, but noauth=true ignores the error and continues installing. The installed dir looks like this:

# ls -l ascii-i386/
total 56
drwxr-xr-x  2 root root 4096 May  4 12:23 bin
drwxr-xr-x  2 root root 4096 Jun 10 13:21 boot
drwxr-xr-x  2 root root 4096 Jun 10 13:21 dev
drwxr-xr-x 31 root root 4096 May  4 12:23 etc
drwxr-xr-x  2 root root 4096 Jun 10 13:21 home
drwxr-xr-x  8 root root 4096 Jan 29  2017 lib
lrwxrwxrwx  1 root root    5 Aug  3 16:37 lib64 -> ./lib
drwxr-xr-x  2 root root 4096 Jun 10 13:21 proc
drwx------  2 root root 4096 Jun 10 13:21 root
drwxr-xr-x  2 root root 4096 Jun 15  2017 run
drwxr-xr-x  2 root root 4096 Aug  3 16:38 sbin
drwxr-xr-x  2 root root 4096 Jun 15  2017 sys
drwxrwxrwt  2 root root 4096 Aug  3 16:38 tmp
drwxr-xr-x  9 root root 4096 Jan 29  2017 usr
drwxr-xr-x 11 root root 4096 Jun  7  2017 var

I haven't started the OS yet, as one needs to make some more steps for starting it in a chrooted environment. Will post a follow-up soon...

# file: my_multistrap.conf
#
# run:
#   multistrap -d /sw/pkg/debootstrap_devuan/ascii-i386 -f my_multistrap.conf
#
[General]
arch=i386

# same as --tidy-up option if set to true
cleanup=true

# same as --no-auth option if set to true; keyring packages listed in each bootstrap will still be installed.
noauth=true

# extract all downloaded archives (default is true)
unpack=true

# whether to add the /suite to be explicit about where apt needs to look for packages. Default is false.
explicitsuite=false

# enable MultiArch for the specified architectures; default is empty
multiarch=

# aptsources is a list of sections to be used
# the /etc/apt/sources.list.d/multistrap.sources.list
# of the target. Order is not important
aptsources=Debian

# the bootstrap option determines which repository
# is used to calculate the list of Priority: required packages
# and which packages go into the rootfs.
# The order of sections is not important.
bootstrap=Debian

[Debian]
packages=
source=http://deb.devuan.org/merged
#keyring=devuan-devs.gpg
suite=ascii