Try this the next time you are on the highway. Open your driver's window. Stick your hand out. Hold it so your palm faces the front of the vehicle at 65mph. How much work is it to hold the hand in place? The same amount is what your vehicle needs to pull your hand through the air. Now multiply by 100 (or more) for the frontal area of any high walled RV.
Sick to a popup. You'll likely still exceed the van's GVWR and GCWR with a large family and 400 pounds of TW.
Another option is if you have another vehicle to tow. Taking two vehicles to a campground that's less than 200 miles each way isn't bad. Most family in the van and dad pulling the RV.