campfire/Assets/Scripts/TerrainModelPlacer.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[ExecuteAlways]
public class TerrainModelPlacer : MonoBehaviour {
    private void Update() {
        if (!Application.isPlaying) {
            // Update is called in editor when values change
            Terrain Terrain = GameObject.FindGameObjectWithTag("Main Terrain").GetComponent<Terrain>();
            Vector3 Pos = transform.position;
            Pos.y = Terrain.transform.position.y + Terrain.SampleHeight(Pos);
            transform.position = Pos;
        }
    }
}