Welcome! Your confusion is quite common based on your observations. RVs are relatively light for their length. They are big boxes of air! This means they are the most difficult type of trailer to tow as they have a lot of frontal and side profile area susceptible to wind.
So, on you what you have. I am a little familiar with Ford products. I had 1999 and 2003 F-150s and towed my current TT with the 2003 for 2 summers. You can likely determine the axle ratio by the axle code list on the driver's door. Then look
here for decoding.
I think under 5000 pounds dry, maybe even 4500 lower is best for that van. That can be anywhere from 16' long to 30' long for a TT depending on construction/materials.