I'm not an Expy owner, but I face similar challenges with my F150. My truck is rated to tow 9200lbs, but my available payload is around 1600lbs. I've been towing a 32' 6500lb (loaded) trailer for 6 years without any issues, but I'm moving up to a 35', 7000lb trailer. Assuming the hitch weight will be around 850lbs, I'll need to carefully monitor my payload.
You'll get a lot of doom and gloom from some people on here, but my take is this...if you stay below all of your critical numbers and drive cautiously (60MPH tops), you'll be just fine. Keep your tow vehicle and trailer well maintained, especially the brakes and tires. Make sure your brake controller is set up and functioning as intended. If the weather is iffy, if the winds are high, slow down. It's all good. :)
