Aggressive behavior help - black lab

So I am at wits end and hoping someone out there might have some ideas. I have a black lab she’s around 6 years old. She’s a rescue I got her when she was right about a year old. As she gets older her personality unfolds more and more and combined now with early onset of minor arthritis in her hip she’s becoming more and more aggressive towards people - primarily men. I am a man for full disclosure. . So here’s the thing about shadow that just perplexes me to no end.... I have taught her DOZENS of tricks she is the smartest dog I’ve ever had she is eager to please loving fiercely loyal she never runs away off leash and is just the best freaking dog on earth ACCEPT for this one thing.... and I cannot correct it. Any time a man gets near her or really anyone showing authority or size (anything she considers a possible threat) she is very aggressive shows her teeth hair up snaps growls even nips at people and in her little mind she’s driving them off and being protective of me and her domain. I scream at her till I’m blue in the face she knows **** well it’s going to make me very angry even before she does it but does it anyway because she thinks that it’s required to keep Strange people away and it works for her because she’s like 70 lbs and puts on a great show. 90% of people run and get back in their car. But here’s the thing. I live full time RV now and we are traveling and in these parks around tons of people and other dogs and I have to correct this. It’s not so much a behavior as it is a personality trait and I am TELLING you that this dog understands the whole situation completely she knows her being aggressive will keep people away and she knows it’s gonna make me incredibly angry at her but she thinks this is required in order to keep them away and is gonna do it anyway regardless of my response. How do I get her to understand that not every single person walking by the camper is out to get her and in fact The vast majority of them would love to scratch her back and pet her if she gave them a chance - I can’t figure out how to correct this. As smart as she is and loyal and everything else it’s the one thing just totally baffles me.... looking for help out there... I had two trainers tell me it’s hopeless but one of them was an idiot and told me dogs don’t have emotions only learned behavior .... pfft. BULL ! The only piece of the puzzle I’ve been able to figure out about her past is that it involves gun shots or loud bangs because she will pee herself and cower in the corner if I so much as pop the little bubbles that come in a FedEx box. New Year’s Eve like right now all the fireworks going off she’s beside herself with fear and it’s all related to the mysterious year of her history before she was with me that I don’t know about. One person once suggested to me someone was trying to train her to be a retriever - that’s what she is a Labrador retriever and probably took her out in the woods to go duck hunting and scared the bejesus out of her with shotguns beat her to an inch of life couldn’t get her to pass expectations and finally surrendered her to a shelter - ultimately I got her. That scenario makes the most sense to me and fits why she hates loud noises and men. But now she’s safe and sound has been for 5 years with me - HOW do I make her understand !!! Please help anyone out there she’s the perfect dog in every other single way and a great travel companion loves the road loves camping but I’m gonna end up in trouble or worse someone bit with her in the RV parks and I can’t figure this out.......