Since you didn't post the model # of the Trimark you have and didn't post a pic, I"m going to take a wild guess that the Bauer BP-12RV might be the one that would be a direct replacement for the TriMark on a Forest River Georgetown back then. Bauers also have been known to be unreliable too so I'm not sure just how much better it will be. Doesn't hurt to try it if it's a direct replacement.
Here are all the measurements and specs so see how it compares with what you have. Or hopefully, somebody with more knowledge than I have will be able to assure you of the proper cross reference: