Changing packer tmpdir

[147]

I'm running Arch Linux Arm on my RPi. I've installed packer and the default build directory is /tmp. However this directory is only 496MB and is obviously not near enough. I would like to change the default build directory for packer from /tmp to ~/.tmp. But I can't make it work. Please help, and excuse my n00biness

here is the part of the /usr/bin/packer that I think is relevant:
$this->bbcode_second_pass_code('', '
# set tmpfile stuff, clean tmpdir
tmpdir="${TMPDIR:-/tmp}/packertmp-$UID"
rm -rf "$tmpdir" &>/dev/null
mkdir -p "$tmpdir"
')

I tried changing the 2nd line to ...
$this->bbcode_second_pass_code('', 'tmpdir="${TMPDIR:-/home/m147/.tmp}/packertmp-$UID"')
and

$this->bbcode_second_pass_code('', 'tmpdir="${TMPDIR:-~/.tmp}/packertmp-$UID"')

but neither seems to work. What am I doing wrong? Thank you.