dave there is also firber glass which now comes made in bondo form i think its called bondo glass, which smooths out nicely and easy to sand. bondo over time might fall out or creak due to heat. the metal to metal dont go smooth and it a lil harder to sand smooth, but it good to fill in dents. on the 70 elkie we used bondo on the firewall to get raid of teh spot welds and any of the other holes we didnt need. the firber glass was used in the bed area and in the rear fender wheels. the metal to metal was used where the sail panel meets the roof. right now we r puttin power vent windows in the elkie along with power windows.