Hitch Weight
Poppa an E350 is a Ford Van chassis so he has a class C.
If you have a 2" receiver, which I bet you do, it would likely be a class III.
Look on the hitch somewhere there should be a tag or stamping giving the ratings.
Good thing is a tow dolly has very little tongue weight to speak of, 200-400lbs I believe. So if the hitch hasn't been abused and all the welds, bolts and frame are in good shape you should be good to go. One thing about the class C MH's is that the chassis has an extended rear portion of the frame to carry the length of the MH shell. These extensions are generally built out of lighter weight chanel than the frame is and this can't carry the bending load of the tongue weight as good as the origional frame rails can so check this location for bending and cracks as well. I know many people tow heavy trailers behind class C's but I have seen a few bent after the origional rails from overloading.
Darrell