Peat moss is acidic. A better top cover suggestion might be a white trash bag cut open, then stretched over the pot and clipped onto the edges,or tied on with rope, then cut a hole in the cover and plant your tomato. You will be able to water at the base, or if you have a self watering pot, just cut a hoe a little small and stretch it over the PVC watering pipe. If your tomato is already in the pot just cut the cover to go around it, and close the radial cut by holding it together with binder clips. The plastic will keep water in and critters out, and keep the soil from splashing onto the tomato when watered.
This isn't the only way, but it is one way that is easy and works.
My definition of insanity; trying to grow heirloom tomatoes in South Florida!