I did okay with a 1500
but wasn't comfortable with the braking, and I went through rotors.
An advantage of vans is that they have a long wheel base.
Even though I don't know the weight of your trailer, it's probably safe to say that a 350 will be enough. Argosys are usually lighter than Airstreams. If it's a small trailer…maybe too much, because a small trailer could get beat up by too stiff of a ride.
There is a good chance that your trailer will weigh more after the modifications.