If you install all the software in root (using sudo), i think no need to add any path in Stamps_config.bash.
only thing i added in .bashrc file stamps/bin like below
open .bashrc file in root
export PATH=path of stamps upto bin (/home/username/stamps/bin):$PATH
then run
source .bashrc
And then run mt_prep_snap in any path, if it comes then are ready to use Stamps.