Thunder? Goes running for something waterproof (11)

I believe the answer is:

groundsheet

I'm a little stuck... Click here to teach me more about this clue!

'something waterproof' is the definition.
I can't tell whether this defines the answer.

'thunder? goes running' is the wordplay.
'running' indicates an anagram (the letters run around to different places).
'thunder'+'goes'='thundergoes'
'thundergoes' anagrammed gives 'GROUNDSHEET'.

'for' is the link.

Can you help me to learn more?

(Other definitions for groundsheet that I've seen before include "What keeps a tent dry" , "protective cover" , "camping equipment" , "campers need it" , "something for campers" .)

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.