I did this using the jungle ruins, especially the guiding light ruin on top. All the meteors were above to harvest them after the purge ended.
Yet i have to warn you that in this particular spot 1 on 5 purges worked. Most of them were stopping in the middle with the message that attackers cannot reach the treasury. It becomes really frustrating if you ask me. I never tried the ruins close to Den. They are way wider and have huge spawn area for purge camps.
In this challenge…
… I had a beautiful purge base in Darfari lands. I did the mistake to create routes with foundations so after lvl8 purges started i was loosing the finishing. It was very difficult to be on time and kill the sorcerer, so until i reach him and kill him one shower already had dropped and break my paths. After 2 minutes the purges were stopping. So i had to think a way and jungle ruins was my best option since then. But like i told you, especially lvl 9 it was omg, they were stopping without any reason. Later on i fixed with @sestus2009 on Wyrms bane the same purge base. We had completion problems to almost all the lvls. So i finally took the decision and never use the jungle ruins again.
Good luck m8 
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