If that is the light I think it is the above is not going to help. One, just one of the lights in my motor home has a standard bayonet base (like an 1156) but your description fits it to a "T". I have found some LED's (Barjan in fact) that will replace it the next time it goes pop but the only place I ever found a replacement for the oem was an RV store.
A quick GOOGLE search found the following page: You can pick from those designs and perhaps figure out what you are looking for:
Halogen Bulbs - GlobalIndustrial.com