I probably should make this post.
If your experimenting, you could make adjustments to lower your voltage in your RV 12 volt system. For actual application, it makes no sense to me. As I see it, even at 12 volts, the $2 LEDs will not last as long as the 9 to 30 volt units. The 12 volt LEDs will last longer at 12 volts than at 15 volts I think.
If the $2 LEDs lasted 10 days at 24 hours a day, they actually lasted quite a long time (240 hours). Most of us only leave one or two lights on for an extended period of time, typically the dining table light and one other. The others may be on for 30 minutes to 1 hour per night. At most that would be 240 camping nights, not bad for $2.
Wayne