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Moonflowers do not produce a tuber. Is it possible that it is mistaken identity? Four o'clocks can resemble moonflower, and they DO produce a tuber. Here is a collection of articles about the four o'clock: https://www.gardeningknowhow.com/ornamental/flowers/four-oclocks/

Here is a collection of article on the moonflower: https://www.gardeningknowhow.com/ornamental/vines/moonflower/

You might have root weevils. Read about them here: https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-root-weevil.htm. Another possibility is tomato hornworm which is active during daylight but hard to find due to camouflage.

The plant produces many seed pods during the growing season. You can control the spread of the plant by picking the seed pods while they are still green and disposing of the pod. The unripened seeds will not germinate.
https://www.gardeningknowhow.com/ornamental/flowers/datura/datura-plant-propagation.htm

This is a good example of the need for naming plants by their binomial nomenclature, or scientific name.

Those moonflowers that are a vine are usually a type of morning glory, as well as many other vines being called a moonflower.

The one that you are speaking of is probably the flower of a Datura! Some can be large shrubs, or Large single stemmed flowers. Knowing the name of them will allow you to find seeds online, or at nurseries.

This article will help you to care for them: https://www.gardeningknowhow.com/ornamental/flowers/datura/growing-datura-trumpet-flower.htm

Growing datura is simple from seed. Just be aware that all parts of the plant are EXTREMELY toxic, and should be kept out of the way of children or animals. This article will guide you on how to do this: https://www.gardeningknowhow.com/ornamental/flowers/datura/growing-datura-trumpet-flower.htm