Scotty,
Gel coat is the shiny/slippery surface on fiberglass and it's applied in the mold when the motorhome or boat is manufactured. However, older motorhomes may not have had gel coat, but the stuff I mentioned (and mention below) will still work. You don't "add gel coat".
Carnuba wax is about as good as you can use to protect gel coat. The 3M products I mentioned contain carnuba wax, but they also contain some grit to remove any oxidation (fiberglass/gel coat will oxidize over time, especially in the sun). So it does 2 things at the same time - the grit removes the oxidation and the carnuba protects it.
When I wax my boat I use a heavy paste wax that has carnuba but no grit. So, if my gel coat is oxidized, I'm using a 2-step process. The carnuba paste wax I use is called Trewax and is available at marine stores such as West Marine Products, but it's unlikely you'll need it for a motorhome.
Marine stores also sell the 3M liquid stuff, but it's much cheaper at Wal*Mart. The 3M stuff comes in different grits, depending on how heavily oxidized the surface is. I'm not sure how much you'll need for your motorhome, but I'd buy a couple of bottles and, if you need more, you can buy it. If you use less, what's left over will be usable next time.