I pull a 2016 Wrangler JKU Sahara 4 door that weighs around 4400 lbs with some fuel and other odds and ends loaded for travel. Our Navion weighs around 10,600lbs fueled and loaded for travel. Together the combined weight is 15,000lbs and the GCWR limit for them is 15,250, so we're under by around 250lbs. We're pushing it, as you say.
As long as you load up both vehicles with everything you need including fuel, and get the vehicles weighed, and do the math, you should be OK. Those 2 suggest a weight around 4100lbs each on the Dinghy Towing Guides. You'll need to know the specific loaded weights of both vehicles, before you try towing either. If the trucks prove a little heavy, you might be able to shed some weight in your Navion, like water for example. It's all about the math, and what you weigh loaded up.
2018 (2017 Sprinter Cab Chassis) Navion24V + 2016 JKU (sold @ ????)
2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
2002 Roadtrek C190P (sold @ 315,000kms)