Thanks for all the replies.
I think I will add floaters that are non-invasive like frogbit or water lettuce for safe measure (and I don't have stem plants so I see no negatives to this solution).
We'll see if I run into any algae problems when I return back to my tank in 3 weeks.
If floaters do not work, I will also implement the window screening idea.
This is pretty much what I did.
Since they were lightly fed shrimp tanks with a mass of floating plants on the surface it seemed to rob the algae of whatever it needed to grow.