I'm an ELK member. We have visited many Lodges in the past 7 years. The website can give info about individual Lodge accommodations or a Lodge in Carmichael, CA. has books with info.
Probably 40% of the Lodges in the U.S. have some sort of RV parking. The sites are as described earlier, from Spartan to quite nice--all for a small donation.
ELKS are a good group of people, and you'll be welcomed at all the Lodges. Actually, they're pretty safe places to park because most ELKS are older and pay attention to who comes and goes in the campground.
We've camp hosted for several years at our Lodge and have had a ball meeting travelers from the entire U.S.
Stop in at a local Lodge and check it out.