The 38 is a very low especially when used with a 14 tooth freewheel. Why not go with a 44? You probably won't even have to change the crank.
Bikeman (and others) carry lots of rings in lots of different bolt circles.
On a side note: What possible reason do you have for carrying 100 pounds in a trailer and then adding more in panniers? Trim down your load! I pack heavy and even I don't lug around 100 lbs of stuff.