There are a few different ways of improving cell signal, even if you don’t have a booster. Get outside of your RV - cell signal isn’t often able to penetrate the body of a vehicle, so try stepping out of the vehicle to get a signal. Find an open space - try to avoid anything that might block the signal, like trees, mountains, or buildings. Higher places also might offer a better line of sight to the nearest cell tower too. Ensure your cell phone is fully charged - a full battery on your cell phone will mean it has more power to send and receive signals.