Thank you @Ash, that did it.
So I made a quick overview:
1. If your SVN server is not running on the default port 22: add a tunnel entry to ~/.subversion/config
Open the file, look for [tunnels] and a line, for example:
sshserver = ssh -p [port where your ssh server is running on] -q
For everybody: add -q if you're getting 'Killed by signal 15' when trying to checkout.
2. Checkout using a absolute path from the remote location
In this example we use the configured tunnel entry from step 1.
svn co svn+sshserver://user@server/absolute/path/to/svn/repository/project/
More background information:
Basic instructions to connect to a SVN-repo over SSH:
From the book 'Version Control with Subversion':