I’m afraid there’s little you can do, air resistance is the main culprit. The best you can do is keep the speed down as suggested. The weight will become most noticeable when you come west and get into the mountains. Then the TV will really be working to pull that weight up the grades.
You’d have to go a LOT shorter and lighter to see any significant improvement in mileage. I get 14 overall with an F150 4x4 5.4 and 3:55 axle. It hard to track mileage towing in the mountains, but I know my worst case was 9. Generally I do a little better than that. But I’m pulling a 16’ 3000# loaded TT. I don’t really know, but my guess is if I were pulling 5000-6000# I’d be a lot closer to 10 than 14. If you’re pulling that big a TT it’s pretty evident that radical a change won’t happen, likewise neither will the improvement in mileage.
Gas prices can be a pain for me, too. But if I want to travel I have to grin and bear it. I try to cut other expenses to subsidize it. I prefer national forest or similar camping so my camp fees are far less than if I used commercial parks. And we don’t eat out a lot, another potentially expensive addition to the trip. So I muddle through that way.