How do those who hold to a literal interpretation of the flood account respond to the criticism that Noah building the ark would be unfeasible?

With respect to the narrow claim of feasibility, I was surprised recently to learn about the existence of Russian disposable timber ships. Wikipedia says that a belyana could be up to 390 ft long. That's not 450 ft, but it's not far off. It also says that the ships were first built without nails or pitch.

In sharing this fact it is not my intention to take a position one way or another about the historicity of the flood narrative.

If you don't accept the underlying premise of this story that there is a God who interacts with his creation and is perfectly capable of doing things that would naturally be impossible (i.e. what we call miracles) then you are going to find a lot more wrong in this story than just the feasibility of building the ark. For example, how did Noah know there was a flood coming (lucky guess?), how did the animals 'know' to come to Noah, why didn't the predator animals eat the others, how did he gather and carry enough food of all the different animals' diets? The list could go on.

There are other stories in the Bible of people attaining miraculous results with limited resources - Elijah and the widow of Zarephath, Jesus feeding the 5000 to name but two.

Why would such a God not miraculously multiply Noah's efforts in building the ark, and also keep the ark safe and seaworthy during the flood itself?

You can look for a naturalistic explanation if you want to, and there's nothing wrong with this. But whether or not we find one says nothing about the credibility of the story.

Well.

Turns out a bunch of Christians "put their money where their mouths are" and actually built the thing. I'd say that pretty well puts to rest any ridiculous claims about it being "impossible".

What about the usual arguments against?

Noah didn't have the knowledge (wasn't a shipwright) or technology

Really? Do we know that? Even if he wasn't, he had plenty of time to learn, perhaps up to 120 years, and metal-working — not just bronze, either, but iron — was known pre-Flood (Genesis 4:20–22). Another issue is that Materialists tend to be Progressives (meaning, they believe that history shows a continual "upward" trend). In fact, this notion has been fairly well debunked, and artifacts such as the Antikythera mechanism show that ancient humans were no slouches, intellectually. (Or look at the Pyramids, Colosseum, or Damascus steel.) The idea that ancient humans were "dumb", or technologically backward, is a Materialist assertion that is not only contrary to the Bible, but is often unsupported by the evidence. The idea that ancients couldn't build mega-structures is so blatantly wrong that it's absurd that anyone would believe such an idea. (Keep in mind, too, the Pyramids were built after both the Flood and Babel, two events that would have had a significant detrimental impact on the level of technology in practice.)

Comparably-sized ships aren't seaworthy

Critics like to point to the Wyoming as proof that the Ark couldn't possible be seaworthy. It's true that the Wyoming sank... after more than ten years of service. The Ark only needed to survive one, and didn't need to try to navigate. Moreover, the Wyoming was built using construction techniques that are known to be problematic (partly because those methods are fast and minimize material cost). Other methods are known to be superior, and there is evidence that ancients had comparably-sized or even larger ships. Computer modeling has also shown that the Ark would be seaworthy, even in waves up to 30m (typical tsunamis might have 10m waves), and that it could tilt as much as 60° and still right itself.

Noah couldn't have built it by himself / didn't have the budget

First off, Noah had up to 120 years to build the ark. That's a long time. Also, he had a family (including older relatives that hadn't died yet) and nothing tells us he couldn't have also hired help. (Noah might have been obscenely wealthy; we don't know. Even if he wasn't, he would have known that any wealth he or his family might have had was about to become worthless, which would have freed him to spend it... and even if that isn't the case, he still had decades in which to work.)

An ancient reader would have readily seen [the size of the ark] as 'obvious' hyperbole

That may be so... but just because something seems exaggerated doesn't mean it is. (To compare to the luggage example, I'm not aware of stable containment for neutronium, but if I tell you my suitcase weighs 400 pounds, am I exaggerating, or lugging around depleted uranium for some reason? If I tell some country hick that's never seen a brick building, much less one made of metal, that I went to the city and the buildings must have been a thousand feet high, am I exaggerating? If I tell you that some war was so bloody there must have been millions of casualties, am I exaggerating?) Anyone that stopped to think would realize that you'd need a pretty big ark to carry all the animals and their food. People close to the event (e.g. Noah's grandkids) would have realized that the recollection was impressive, but still real. To be fair, there isn't really a refutation for this, other than that sometimes reality is impressive.

Really, though, the most convincing response would be to go out and replicate Noah's construction. And we did.