I can't tell you the number but the Pemex is about 4 miles south of Los Mochis and is very large - you can find it on Google Earth - we have stayed there several times and there has always been tons of room - there is a security guard and it is totally fenced with two electric gates - they have a small restaurant and I think they even have showers - on the west side or southbound - I do not think you can still turn in from northbound as I think the build a barrier in the middle of the road. We do not like the RV park in Los Mochis or either of the truck stops up there - this one is relatively quiet. One of the trucking companies - maybe Bimbo bread - uses this lot as a relay drop and pick for trailer and tractors going in opposite directions - other than that not much going on whenever we were there.
Try these numbers.......
25.78303° -108.87615°