coolant leak 3500 van

I have a small rv based on a 3500 chassis and a 6.0l v-8 engine. I ran the engine yesterday to lubricate it after sitting for most of the winter. After running for about 20 minutes I shut it down. Later I noticed a very small amount of coolant on the ground. I looked underneath and saw a small drip on the oil pan. I wiped it off and it did not return. Is this a leak to be conerned about? It only seems to occur when the engine is warm and the coolant level in the tank has not dropped. Is it normal for a little coolant to leak after sitting and is first used? Thanks