I'm now at the age when I don't have to worry about spontaneous erections in the gym showers. If anything I'm trying to fluff up. There is only one open shower I can think of. It used to be one room with about 10 shower heads. Now 3 of the heads have had cubicles built around them. When ever I've used that shower room I'm often the only one in there. I remember the time when open showers were very busy and maybe 1 or 2 guys were waiting on a shower head, standing outside the entrance nude. My how times have changed.
I belong to two gyms. The Planet Fitness has cubicles with curtains. Across the from the shower cubicle is a small one person changing room. So you can finish your shower, wrap a towel around you and walk across to the changing room with your underwear in hand and towel wraped around you and no one can see your naked body. That isn't how I fly
I've been going to open showers and locker locker rooms since school days. I have no problem being naked in showers, saunas or steam rooms. I've been showering with others in the military and gyms for several years. No shyness here.