We asked if they had experienced any camping difficulties.

a.

participle

b.

gerund

c.

infinitive

It would be A; participle.

If the idea is to classify the word "camping", it can be said that the correct option is A participle

This is because it comes from the verb "camp" and it functions as an adjective because it is modifying "difficulties"

In the case of a gerund. it would function as a noun and the infinitive form does not have the ING inflection.