The sombrero is light yellow, dark green, and red-orange with red circles dangling down from the flat part in "Idiot Box." In "The Camping Episode" it does not include the green swirl across the middle and does not include the red stripe at the top. Instead, it has yellow and green circles dangling from the flat part of it.
In "The Camping Episode", Squidward is tries to scare SpongeBob and Patrick by doing things to attract a sea bear, but it actually does make a sea bear appear, which attacks him. It also appears "Idiot Box," when he was looking for a box to sit in.
"Idiot Box" must take place before "The Camping Episode," as Squidward says after taking it out of its box "Why haven't I worn this yet?," unless he was referring to a different sombrero.