My new 2107 E450 wandered a bit when I drove it off the lot. However, from studying Class A's and C's for over a year before purchasing, I knew one of the first things to do was to get an alignment with as much positive caster as possible. In comparison to the brief bit of pre-alignment driving I did, there was definitely a large improvement in steering slop at highway speeds.
Before the alignment you do want it loaded as it would normally be loaded, and if you have rear air bags have those adjusted where you want them as well.
Other improvements you may want to consider can be found here (what I did you my Class C is in post #19...lots of other good info from others this thread): Class c highway handling