Seeing as you can mail a coconut with just its outer shell through the US postal mail system without any packaging/wraping(It's true!), my guess is it’s going to be fine, even if you just have the inner seed in your luggage it would take a lot of pressure to crack it, have your ever tried to open one without mechanical means?, its tough.

My guess is your main issues are going to be with the country custom’s law in importation of fruit/seeds if your crossing international territories while bring those coconuts back, not with how you are storing/transporting it.