No it won't do any harm going down in size on your converter, but why would you want to do that?
I suppose it depends on how you camp and how many appliances and lights you plan to use. The converter converts 110 to 12 volts to power most of the stuff in your trailer. It there is anything left over it will charge the batteries. As long as you are plugged in, it shouldn't matter much. Your converter can always charge batteries at night.
I dry camp a lot and often use my generator for a few hours at a time. I have a 55 amp three stage converter. I can run lots of stuff in the trailer and still be able to charge the batteries. If I had a much smaller converter, it might take longer to keep the batteries up.
But no, it won't hurt if you move down in size. Are they that much cheaper?