For our first year (2018), we used the CoPilot GPS app on our iPhones. It stores maps locally and allows you to input RV dimensions and weight in and will route accordingly. However, after an update to the app this year, it started doing some really crazy routing (get off this exit, do a U-turn and get back on, etc). Coincidentally, the next week, Eric from TechnoRV asked if we wanted to try a new GPS. So glad you asked!
Since February (2019), we've been using the Rand McNally OverDryve 7 RV GPS and LOVE it! Great big display, voice prompts (that aren't overbearing), and it finds rest areas, service stations, etc along our route with ease! We will have a full review coming out soon!