If you want the gem rewards from reaching Master, I don't really think your TH8 base would matter that much. Why?
1) Once you reached Crystal, it's hard to win a defense, so almost all of your trophies
will come from your attacks.
2) Everytime you logout, TH9 and TH10 bases that you attacked will revenge you immediately, and you can be certain that it wiil be 3-star more often than 2-star.
Knowing this, I think the best you can do is to prevent a 3-star attack due to
lack of time. I would try to distribute my structures strategically througout the whole map so that common attackers will not have enough time to 100%.
However, I'm still not sure how well a maxed def and walls TH8 base is in defending against TH9 and Th10 revenging armies. I did my pushing to Master when I was still TH7 and my base didn't really matter.
If you just want to reach Master, offense is enough.Your defense is for staying there.
