You can mount directories in dosbox with mount command in dosbox command line. For example
mount c /home/user/MyDocs/dosbox
would map given folder as drive C:. You can put commands that are run on startup to the dosbox's config file in section [autoexec]. You can put the mount command in that section and have your folder mounted automatically. You can also put c: to the next line so you would be located at the root of c-drive on startup.