Camping is not an adjective. Camping is a gerund, and hence a noun.
Adjectives are words that describe or modify other words. They can identify or quantify another person or thing in the sentence. Adjectives are usually positioned before the noun or the pronoun that they modify.
As part of a phrase like camping trip it is a noun in apposition, modifying another noun as if it were adjective.
In a sentence like He is camping it is a present participle, which is used in forming the progressive tenses, but may also behave like an adjective: The camping girls slept soundly.