we replaced 3 lights on one of our campers and the brake lights had 1157 bulbs. only thing we learned was when you take the covers off it breaks the seal, and if you dont seal it back then it will leak and they will short out in a short bit. so make sure the covers are sealed !
I replaced all of mine when I redid the aristocrat.I just pop the cover off and removed the 2 screws. You willl want to be careful and not let the wire go inside the wall. Make sure everything is sealed up good. I put my new ones on and I had not reinstalled the inside paneling. I was glad I had 1 leak. It leaked into the cover and then went behind the light. I resealed it and it was fine. I far as the lights goes You probably will have to take your off to see what you need. I have seen a few diffenrent bulbs used. 2-3 that I know of. One type are the round based ones and I think the ones I have now are square based.
I replaced all the marker lights on both sides and the front. It made the camper even look much better w/shiny light covers.
Ken