I love the Ecoboost, but towing weight it not the problem for them, or any difference between a TT and 5er. Payload and pin/tongue weight is. I only recommend the F-150 with HD payload package for 5th wheel RVs.
8000 pounds loaded TT = ~1000 pounds of TW, of which about 800-900 is on the truck's axles against payload.
8000 pound 5th wheel is ~1600 pounds of pin weight plus a 200 pound receiver against payload. Very few half ton on the streets have 1800 pounds of payload, let alone another 500+ for people and cargo.
Plan your RV/TV together and carefully. Learn the compromises of 5er vs. TT, and generally <7k loaded RV and higher.