I am a th 7 with max barb king and minions
I did it fairly easily by going to around 1400 trophies with 9 drags 20 archers and 3 rage spells, all max level. Hit bases with over 1.2k de, 1k if you aren't finding bases with 1.2k. Try not to use all 3 of the rage spells unless absolutely necessary. I attacked from the side defended by the least number of air defenses, or the side closest to the de, whichever was more convenient. This army basically guarantees you get the de from any th that has level 5 air defenses or lower and no inferno tower covering the de. It is relatively efficient too, considering that it takes the same amount of time to train with 3 max level th 7 barracks as it does to make 3 lightning spells. Faster if you have all max level barracks and do 8 dragons with 40 archers. Probably the best you can get in terms of efficiently collecting de for th7, providing elixir costs are of no object.