You forgot the photo.
Since you have an F-450 with 19.5" tires and 10 on 225mm hole pattern, forget everything I said in my early post.
To get by cheap, you could just remove the outside tires and keep the inside ones.
Then peal off the dually fender humps and have any body shop smooth out what remains, or maybe add fender flares similar to the ones used by the off-roaders. That would reduce your rear GAWR to 7,500 pounds. But a 14,500 pound 5er should have only around 2,600 pounds of hitch weight. That leaves 4,900 pounds max rear axle weight without overloading the single tires. And your wet and loaded truck without the 5er tied on should have a lot less than 4,900 pounds on the rear axle.
Of course, the better (but more expensive) fix would be to buy new wheels and tires that wouldn't look phunny when going down the road. You probably won't find any SRW wheels with your hole pattern of 10 on 225mm, so you'll need to order custom wheels from somebody like Rickson or Stockton. And your stock wheels are only 6" wide, so the biggest tire you can safely run is LT225/70R19.5. But with custom rims you could move up to the super single size of at least 245/70R19.5.
For example, if you ordered new wheels 19.5" diameter and 7.5" wide, you could go for the Michelin XZE2+ tire in size LT285/70R19.5. About the same as the old 35s in diameter, with 6,395 pounds weight capacity per tire, or 12,790 pounds on the rear axle. That's more than you'll need with your 14,500 GVWR to not lose any hauling capacity when you go to the super single tires.
If you have the 4.88 axle, you'll probably love the taller 285s, which will give you the equivalent of a 4.45 axle ratio. Or if you have the 4.30 rear end, then the taller tires will give you the equivalent of about a 4.10 axle ratio. You'll probably like the 4.10 ratio just fine except for dragging your trailer across the Rockies on I-70 or I-90.