You are maxed out on weight, but that's not the only concern. There's a big difference between 15,000 pounds of bolts and 15,000 pounds of hay. Though it's the same weight, the hay will be much harder to tow than the bolts. RVs are like hay, not bolts.
I'm towing an 8,000 pound 37 foot long travel trailer. It's technically a "half ton towable" trailer, but I wouldn't dream of trying it. I could tow it with a 3/4 ton and be okay, but it's way more than a half ton can handle. The problem (for both of us) is the size of the RV. It's tall, and long, and in your case, you're trying to keep the pin as light as possible. That's a recipe for disaster. It's going to catch the wind very easily.
With a 3,000 pound advertised pin weight, you're looking at a 15,000 pound or more toy hauler right? You can tow that with a SRW, but it's going to be a rough experience. A DRW will control it far better than a SRW. For that trailer, you need a DRW. If you were talking about a 35 foot, 12,500 pound RV with 2,500 pound tongue weight, I'd be fine with a SRW, but not one as long and heavy as you're asking about.
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