We use the big Pemex truck stop just south of Los Mochis as a convenient stop between Guaymas and Mazatlan. It is Pemex #4925 and has a huge rest stop for trucks, with 24 hr security. It is very busy and very dusty but it works. Alternatively you can stay at the Copper Canyon RV Park in Los Mochis, also affectionately known as "the rooster park" (you'll figure out why at sunup each morning :)). It's reasonably priced and has been spruced up a tiny bit in the past couple years. It's still not much of a place but it's a place to stop.
If you haven't looked at Dot & Bill Bell's website, have a look here:
Mexico RV travel It's the best online information on Mexico RV Travel that you will find.