Learn Dutch: Die vitrine moet verzegeld worden, opdat de vochtigheid laag blijft. - That display case must be sealed, so that the humidity remains low.

Yes, and in everyday speech, you almost certainly would! Opdat means exactly the same thing as zodat ("so that" or "in order that") but is much more formal. It strongly emphasizes the intended purpose and is mostly used in written Dutch or official contexts, like museum guidelines for a fragile display case.

Why does the verb blijft go at the very end of the sentence?

Because opdat is a subordinating conjunction. Just like omdat or zodat, it introduces a dependent clause, which forces the conjugated verb (blijft) all the way to the end of that clause.

Why do we need worden at the end of the first clause?

The first clause uses the passive voice with a modal verb (moet). The literal action is "must become sealed". Moet is the conjugated modal verb in position 2, pushing the rest of the verb phrase to the end. Because it is a passive construction, that pushed phrase is the past participle verzegeld followed by the infinitive worden.

What is the difference between a vitrine, an etalage, and a raam?