being fired for not going on trip for convention.

I think you need to write a letter to your boss, that very politely says that the constant sexual remarks and behavior make you very uncomfortable.  You should also say that because of the history of all of that, the idea of being in the car, in the hotel on this trip with the three men makes you extremely uncomfortable, and that this is why you have refused.  Insist, again politely, that the staring and the comments come to a stop, immediately.

Make sure you keep a copy for yourself, and I'd make sure you get a copy of it out of the company's control before you hand it in.

If you're fired, and maybe even if you're not, I would very strongly recommend that you have a consultation with an attorney who specializes in employment discrimination cases.  These can be difficult, and they are very fact-sensitive, but the outline you've provided in your question suggests what might be a very strong case of sex discrimination by means of a hostile work environment.

You may also file a complaint of sexual harassment with the federal Equal Employment Opportunity Commission (EEOC).