Shocks control the bounce, if you will, of the vehicle, while the springs (be they coil or leaf) handle the weight of the vehicle (including the tongue weight.) Some shocks have coils over them and these will help with the sag somewhat, but you should have someone qualified check your springs to see if they need attention. As stated above, can you be a bit more specific in what you are experiencing while trailing? It could be that the use of a weight distribution hitch is all you need, but it would help to know more.
1975 Westfalia (VW)
2014 Rockwood A122