Good point. I also tow with max air pressure. I was always told that trailer tires do not fail from weight. But from speed and low pressure producing heat. My trailer is also a tilt bed (meaning it has two frames) and weighs 3200 pounds, so I don't get much bounce even at max pressure on the tires.I have a GR L6060 also and when I do the math on weight I was over loaded on my 10000lb steel trailer. I came up with close to 10000lbs loaded weight. Now, that was with my forks on the front tied down, tractor, loader and backhoe and I also have loaded tires. I took the weights listed in owners manual not actual scales. I purchased a 14000lb steel trailer, to make me feel better. I also tow my Kubota zero turn on it more than my 6060. I have been doing this for a couple years now with no problem. I also run all my trailer tires at max psi. Yes, they do ride a little rougher. I also don't think a few psi will make that much difference on a 10 ply tire. (YMMV) Most usually when you see a trailer on side of the road with a tire completely blown out. It is because of low tire pressure. The aluminum may be more prone to cracking from bouncing than steel. I would ask the salesman to explain what damage could be done by towing empty, he may know something we don't. Good luck with what ever you decide.
This might be right - If they were worried about cracks, and if that is the case, I personally would pass on al. That is why I try to purchase trailers from manufactures that use only certified welders. My L4701, FEL, box blade, pallet forks, tool box with tools, 7 ratchet binders and chains weighs right at 11k. Best Wishes.