The 3500 was the range I had seen on a lot of posts, primarily due to the frame extensions. It might depend on the unit itself.
Gale, thanks for the info. My car trailer is great, but it's 8.5 x 20' and steel, so it's heavy. The cobra only weighs 2000lb. I have considered dropping down to an open trailer aluminum, but I'd rather have an enclosed one.
To get a diesel, I might have to spend $20-30k minimum, and stick to mid-90's. The nice thing is that it seems like getting a slide out would be more likely.
I do believe you can have new frame extensions added or the originals beefed up, which increases the tow rating without going over GVWR. It seems that a lot of the 4x4 guys have done this to their class c's.
I just bought a second Cobra, almost done with my paint and body work on the first one, the new one will be a resale car, after I do some rebuilding on it.