Welcome Aboard! Nice looking 5ver.
Your fully loaded pin weight (4,139#) should be about 20% of the GVW (20,695) of your fiver. You may never have it fully loaded, but you should plan for the max pin weight.
Toy haulers in general can be a bit screwy from a hitch/pin weight calculation, as they figure your going to have something in back, but what? How heavy? Per Jayco's website, the empty the pin weight of that Seismic is about 23.5%. Looking at the floor plan all the fixed weight looks to be forwards of the axles. If you only add personal items in the kitchen and forwards, the pin weight can get really increase quickly. Having a bike or other heavy items in back, could be helpful.
Quick look at Ford's Payload capacity chart, your talking at least a 1 ton dually, and only a few configurations look as if it might work. Probably more like a F450. Sure Chevy and Dodge will be in the same ballpark.
Sure looks nice