If it's a Ford chassis it does not have ball joints. They use kingpins. They could be worn but not likely. Inspect the bushings where the two axles meet the chassis crossmember.
We had a Holiday Rambler on a 1983 E350. It was all over the road until I:
1. Added a rear leaf to both of the sagging rear springs
2. Replaced the front sway bar end bushings
3. Set front wheel toe to slightly "in" since I found it way "out"
Weigh it if you haven't and set pressures according to the load using a chart. Excess front tire pressure and it'll wander.