As long as you stay in your home state, farm plates will probably work on the RV. However, once you cross state lines, the other states are going to want you to stop. Now,what do you do? You have a truck, licensed for farm work, pulling a RV? Not licensed right. That other state will want license, and money.
I have heard of some doing both. License farm, and also license as RV. Not sure how works, but that is what they say. Change plates when change to RV. ??
Just check it out before you go to another state. It might get expensive otherwise.