Just did a 400 mile round trip with my 22' travel trailer. The tires are original cheap 2 ply with 32 psi max inflation. Not happy about taking it offroad as we did to a bear hunting camp location on a landing overlooking a clear cut. Absolutely great spot for privacy and beauty. We could sit in camo chairs and glass for bears, deer and elk. Anyway, my question. Obviously with some 6 ply or greater offroad LT tires I'd get better braking traction and puncture resistence. We were lucky and didn't get a flat. But could I also expect a slight increase in fuel economy with tires inflated to say 55#? Sidewalls on current tires roll quite a bit when turning and puncture inevitable. 7,000 GVW trailer. Great success with the tow vehicle as well! The vehicle has a canopy that's 14" above cab height. 17 mpg while freeway driving. Fuel pump never fell below 15 psi. Kept the speed at 55 mph or less. Avoiding shift downs as much as possible. Combined fuel milage of 13.5 which included hiway and low/high range 4x4 work on forest roads. Forgot to add that this mpg was partial hiway with trailer, and a lot of running around in the woods without the trailer.1,000 watt Honda generator kept batteries topped off well when we ran it in the evenings. Furnace came on a few times at night. This was the first boondocking trip I've made with this trailer. Everything worked great! Rained a bunch. Was nice to be dry, have hot water and a dry place to both sleep and socialize. Awning was very useful too. Camp chairs outside stayed dry and is nice to have more room to escape the trailer space and stay dry.

Load Range D's would fit you bill just fine. I've got D's on my RV with a GVWR of 8,500#. They have a maximum inflation pressure of 60-65 PSI. Personally when it comes to a new set of tires I'll up size mine from Load Range D's to Load Range E's...

Sidewalls on current tires roll quite a bit when turning and puncture inevitable. 7,000 GVW trailer.

This is inevitable with low load-range trailer tires, especially with multi-axles. the sharper you turn, the more they roll over, wear the edges out, and so on. A heavier load-ranged tire will help with the roll, to an extent, but will be less likely to tear up like cheaper, lighter tires. Trailer tires are just not designed for "low speed, high drag", if you will.. ;)

I put a set of DURO radial 6 ply tires on my fiver over 6 years ago and they are they are doing great! I just did a brake inspection and the tires are almost as good as new. I don't go off road, but they are not showing any signs of age yet. I would recommend them.

My trailer is 8k lb, an 04 built in 03. It came with Maxxes 8008 load range D tires. I put 3k-4k mi a year on them and they still had a lot of thread left, so that's 9 yr and about 36k mi. I replaced them last year due to sun rot with the same make and model. That's right, I didn't keep them covered....:banghead: I've taken it over a lot of dirt roads with no problems and tire pressure is 50 psi.

The hard part is finding load range D with 14" rims. Very limited selection.

Is there any way to put 15's on ?

I had LRC 14" tires on my 18CK, GVW 5,600, 205/75/14 Goodyear Marathon's rated for 1760 @ 50 psi. They worked great on lots of dirt roads. Over a period of 4 season and probably 30+ trips (only maybe 1 per year didn't see any gravel) I only had 2 flats. I am not sure a LRD tire would have alleviated the flats, based on the rocks that did the punctures. The GVWR was lower, but a LRC is a 6 ply "rated" tire that will meet the needs of the 3500lb axles I am guessing you have. They also hold 50 psi. I don't recall being able to find LRD tires for 14" rims.