Towing any high walled RV takes quite a bit of power to pull two sheets of plywood through the air at 60-65mph. A naturally aspirated V6 with 253lb-ft of torque will be towing at 3000rpmm vs. the 5.0L V8 at 2200rpm. Add any freeway overpass, hills, mountains, and they both will shift down a gear or two. So for the same desired speed, the V8 will be running about 2/3 the engine speed of that V6.
The Ecoboost offers peak torque in the 2000-2500rpm range, so it will not need to downshift much as even the 5.0L V8, just increase turbo boost. That's why owners love the Ecoboosts (and turbo diesels).
I recommend the 2.7L Ecoboost for your desired RV.