One of the first things I check when looking is how much carrying capacity remains with ALL tanks full. A 100gallon black tank is useless if it's unsafe to tow full. Over the years I've seen many that would be overweight (sometimes horribly) if the tanks are full. I'm sure they justify it by claiming you'll never have all tanks full, however that's BS unless you plan on never adding water to the fresh tank while camping.
I would move on. There are tandem axle trailers in the 17' class by Nash and I think Winnebego TT's.. probably others.. that should afford more carrying.
Our cheapo Econ 16RB single axle even after upgrading black from 5 to 25 gallon still has 400# of carrying capacity (that's based on actual ready to roll weight).
