Using 5200 on threads guarantees they won't come apart unless you use a torch. And you won't be able to pull the hose off the barb.
5200 for the thru-hull-to-hull joint;
Teflon pipe-joint compound, or heavy-duty (pink) Teflon tape for the threads.
If the barb is good, just a pair of tight AWAB-brand hose clamps (All 300-grade stainless, very durable).
That way, when you (or the next owner) want to take it all apart, you'll be able to.