I tow a 4k lb trailer with a dry tongue weight of about 400. With my setup, I have another 100lbs on the tongue max. If you have a "dry" tongue weight of 815, once you get propane, a battry or two, and then the normal trailer load. . .god forbid any actual fresh water, etc. . .you are grossly over the limit for the LR3. Just my two cents, but that would also be demonstratable negligence on your part. If you got in an accident and hurt anyone. . .say good by to your life. I would prosecute and sue you to nth degree.
Not that I would do it, but 600lbs may be plausible. . . You are likely well over 900lbs actual trailering tongue weight. Way out of the LR3 capacity. I wouldn't even try this once.
Not to mention, the wheelbase of the LR3 is only 113". . . A 26' trailer with the weights you mention. . .I would not be surprised if it had its way with you poor LR3. Don't get me wrong, I was shocked at how good my LR3 tows my rig. . .but it is well within the reccomended guidelines, and is only 21' long. Never had a white knuckle moment yet with my camper. . .