Free accommodation: When travelling we spent time using the app “walmart near me”, some Walmarts that are not privately owned allow you to car camp overnight in their car parks. This is handy as a lot of them are 24 hour supermarkets so access to toilet facilities are available.
Showering: We got a monthly black card subscription to Planet Fitness, this allows you plus one guest to use their facilities,. We would go in a do a workout and shower, the good thing with Planet Fitness is there is over 2000 stores in the USA so when travelling outside of the National/State parks they were readily available. For the ladies they usually have a hairdryer, you can use the hydro massage beds and tanning beds. All for $23 a month so a good option only if you use the shower facilities.
Other showering and free accommodation options are the travel plaza’s located mainly along the international highways. You can park there normally with a lot of trucks but they offer showers for around $15, a truckies lounge and most have a diner attached. Some groups are Pilots, Loves and TA.