On the ventral seam, there are small drain holes along the fuselage ventral centerline, and there should be one in the bottom of each wing stub (not present on the kit parts). The only rectangular hole I know on the dorsal centerline is one immediately in front of the cockpit. That hole is used to mound the windscreen. James Fahey (JAMO) has some excellent photos of one of TVAL's Albatros D.Vs. Do a search to find them, or hopefully, someone has saved the URL to the topic(s) with the photos.
Hope that answers your question.
Bill