Need to have oil changed in our Ford 450 engine class C RV, should it be done before we park it in RV park for 4 months or wait until we get ready to leave in April?

It's more of preference of doing it before you park or before you leave. It wont matter if the old oil sits or the fresh oil sits for only 4 months. Oil does break down over time even sitting but I wouldnt worry about 4 months.

Call their service department Debbie

I say before as well

Better answered by a mechanic, but my opinion is before...