If you've recently become a solo person (divorce, break up, etc.), then I suspect much of your anxiousness and feeling like a "loser" is due to your emotional state. In that case, I would say give it time to adjust to your new circumstances.
Find new hobbies and interests and find ways to incorporate your RVing into them (or them into your RVing).
Start small. Go to the movies alone, go to a local museum, etc. Doing things alone around home will help you realize that not only are people not judging you, but they really aren't looking at you at all. Experiment with things - try a matinee movie instead of an evening showing; try going out to breakfast rather than dinner. Find ways to keep your mind occupied on the sights rather than thinking about your status - photography is a great way to focus on the sights.
If you make reservations for campgrounds (or hotels), just use 2 persons by default. It's not going to cost any different and it's nobody's business. If once you get there someone questions, just say "oh, my friend is going to try to make it up later". No biggie.
Remember that most family groups are going to stay together and aren't usually that open to outliers. Older couples and pairs/groups of women are usually a bit more welcoming. Other solos can go either way - some love their solitude, others are eager for company When out on hikes, have a hello for folks as they pass. A simple "there's a great view about 40 yards back" can open up a conversation. As a solo man, there will be more hesitancy from some people, just accept THEIR issues and go on your way.