Sad to hear of your loss. I suppose I don't need to say, now, that ducks are very likely to get killed by predators unless you have a sturdy, secure area for them.
Please take a look at this topic:
https://www.backyardchickens.com/forum/viewtopic.php?id=178796
Especially note the one at the bottom of the first page - I think you should be able to put this together pretty easily. And for just a few ducks I think it would work nicely. But do read more, about the ways that predators have of getting past barriers and incorporate the ideas. I use two strands of electric fence - equine tape - and I know for sure it's zapped two raccoons this year.
I use half inch hardware cloth over any and all openings in the night pen. I also, by the way, just have them in a pen in our walkout basement. No, it doesn't stink. I use straw, add a little each day for a week or so, and change it all out when it begins to smell earthy.
It is important to manage their water (I give them water 24/7), so I have their bucket in the bottom of a plastic dog crate, to catch the splash.
Anyway, now that you've seen the heartbreak predators can cause, please do take advantage of all the knowledge and experience here.