Due to the lack of a built in solution or a (simple) plugin which connects a SVN-repository and Mantis, the connection of these two system could be a bit tricky.
Preconditions
These system could be but must not be on the same host.
Configuration SVN
Add a post commit hook to your SVN-repository with the following code:
#!/bin/sh
REV="$2"
URL="http://mantis.example.com/plugin.php?page=Source/checkin"
PROJECT="ProjectName"
CURL=/usr/bin/curl
${CURL} -d "repo_name=${PROJECT}" -d "data=${REV}" -d "api_key=4289def1asdc402abf71de1d" ${URL}
Configuration WebSVN
Add the repository to WebSVN, which is use to see the source of the code and the diffs of the commits.
PATH_TO/websvn/include/config.php
$config->addRepository('$NAME', 'svn://URL_TO_REPOSITORY', null, '$SVN_USER', '$SVN_PASSWORD');
Configuration WebSVN
Add the repository to Mantis.
Commit message commands