I don’t know about the composition of modern condoms, but at least, they used to be made of latex (natural) rubber, which deteriorates and goes gummy, when exposed long-term, to the oxygen in the air, and/or oils. That’s why they were factory-dusted with talcum, and came packaged in sealed foil. As a short term protection from water/moisture in the field, they’ll do. But as a long term ready-to-go cover, they’ll deteriorate. Keeping a small roll of electrician’s tape spooled on the barrel, ready for the next outing, seems to me a likelier solution than a partially-congealed, stuck-on, condom.