sono ryokou ha sukkari dainasi ni natta.

Because その is a determiner that directly modifies a noun, like that in English.

• その旅行 = that trip
• この本 = this book
• あの人 = that person over there

You do not use の after その / この / あの when they come before a noun.

By contrast:

• それ = that one
• その旅行 = that trip

So その must be followed by a noun, while それ can stand alone.

は marks その旅行 as the topic of the sentence.

So the sentence is talking about that trip, and then saying what happened to it:

• その旅行は = as for that trip...
• すっかり台無しになった = it ended up completely ruined

In natural English we usually just say That trip was completely ruined, but Japanese often uses a topic-comment structure instead of matching English subject structure exactly.

Because なった shows a change into a state.

• 台無しだった = it was ruined / it was a mess
• 台無しになった = it became ruined / it ended up ruined

The verb なる means to become.
So:

• 台無しになる = to be ruined, literally to become a ruin/mess

Using なった emphasizes that something happened and the trip ended up in that bad state.

台無し means something like:

• ruined
• spoiled
• wasted
• messed up

It is used when something that should have been good, useful, or valuable gets spoiled.

Examples:

• せっかくの計画が台無しになった。
  Our carefully made plan was ruined.
• 雨で試合が台無しになった。
  The game was ruined by rain.

In your sentence, 台無し describes the trip as having been spoiled or ruined.

Because なる often uses に to mark the resulting state.

Pattern:

• A は B に なる = A becomes B

Examples:

• 春になる = to become spring
• 元気になる = to get well / become energetic
• 静かになる = to become quiet
• 台無しになる = to become ruined

So in this sentence:

• 台無しに なった = became ruined

The に marks what state the trip ended up in.

すっかり means completely, entirely, or thoroughly.

It strengthens the sentence:

• 台無しになった = was ruined
• すっかり台無しになった = was completely ruined

It gives the feeling that the damage was total, not partial.

It behaves a bit like a noun and a bit like a na-adjective.

You can think of it as a word meaning ruin / uselessness / a ruined state, and it appears in patterns like:

• 台無しだ
• 台無しになる
• 台無しにする

So in learner-friendly terms, it is often easiest to treat it as a na-adjective-like word or a noun that can describe a state.

What matters most here is the pattern:

• 台無しになる = to become ruined
• 台無しにする = to ruin something

This is an important contrast:

• 台無しになった = became ruined / ended up ruined
• 台無しにした = ruined it / made it a mess

So:

• その旅行は台無しになった。
  That trip was ruined.
• 彼がその旅行を台無しにした。
  He ruined that trip.

The first focuses on the result.
The second names the person who caused it.

Japanese often leaves out information if it is obvious, unknown, or not important.

This sentence only tells you the result:

• The trip ended up completely ruined.

It does not say who or what caused it. That could be understood from context, or the speaker may simply be focusing on the outcome rather than the cause.

If you wanted to mention the cause, you could add it:

• 雨でその旅行はすっかり台無しになった。
  Because of the rain, that trip was completely ruined.

Yes, to some extent. Japanese word order is more flexible than English, especially with adverbs like すっかり.

These are all natural:

• その旅行はすっかり台無しになった。
• その旅行は台無しにすっかりなった。 ← unnatural
• その旅行は台無しになってしまった。 ← also natural, with extra nuance
• その旅行は本当にすっかり台無しになった。

The most natural placement here is exactly what you have:

• その旅行は すっかり 台無しに なった。

So yes, Japanese allows some flexibility, but not every rearrangement sounds natural.

Yes, depending on context, that can work.

台無しになる can mean:

• to be ruined
• to be spoiled
• to go to waste

For a trip, the most natural translations are usually:

• That trip was completely ruined.
• The trip was totally spoiled.

If the emphasis is on wasted effort or lost value, went completely to waste can also fit.

They are:

• その = that
• 旅行（りょこう） = trip; यात्रा/travel
• すっかり = completely
• 台無し（だいなし） = ruined; spoiled; worthless
• なる = to become

The sentence uses the past form of なる:

• なる → なった

So:

• 台無しになる = to become ruined
• 台無しになった = became ruined / was ruined

It is plain, non-polite style, but not rude.

• その旅行はすっかり台無しになった。 = plain style
• その旅行はすっかり台無しになりました。 = polite style

The plain form is very common in everyday conversation, storytelling, and writing.

A native speaker would usually hear something like:

• the trip was supposed to be enjoyable
• something happened
• as a result, the trip was thoroughly spoiled

So the sentence carries a sense of disappointment. It is not just neutral description; it suggests that the trip lost its value or enjoyment.

In other words, it sounds stronger than simply saying the trip changed or the trip was bad. It means the trip was basically spoiled as an experience.