Probably the easiest is the Nugget in Sparks as it is just off the freeway at Pyramid highway.
East of Sparks a bit is the Wadsworth rest area just past Fernley on I80 westbound. It has wifi and an RV dump. Stays are allowed up to 18 hours at Nevada Rest Stops.
On the west of Reno is Cabellas and I believe they have overnight parking as well. They are just off the freeway very near the California line and the only gotcha with access is taking care to follow the signs at a roundabout so you take the right road.
On I80 through Reno and Sparks do watch out for right lane exit only's. They are well marked but you'll have an easier time avoiding the outside lane, I think.