The "Geo method" worked great for keeping the sensors functioning on my 15-year-old black tank.
But even that doesn't "freshen" and "deodorize" as the OP requested. I have to agree with the other posters who say that those are not reasonable goals.
I always call ahead, as noted earlier you never know when a policy has changed due to anything from new local regulations or maybe parking-lot repaving.
But I don't understand this insistence on talking to the "manager." Surely he or she has better things to do, and surely all the employees know their store's policy. I just call the store's phone number and ask the person who answers the phone, "Does your store allow overnight parking for customers who have RVs?" This has never gone wrong.
I'm so glad to read that you've decided to go. Remember that in addition to the 50% chance of rain, there's also a 50% chance that the weather forecast around here will change completely every 24 hours. And also a 50% chance that the afternoon weather will be completely different from the AM forecast.
Just be prepared for any combination, including walking or biking with sun overhead and mud underfoot.
… We are thinking about a 25' Class C without a toad….. Would it be unreasonable to unhook everything to go to a restaurant or maybe go sightseeing and then hook back up upon return? … .
I've done exactly what you plan to do, and I found it perfectly do-able. A smallish Class C can find a place to park in most parking lots (stores, restaurants, etc.) or even park on the street. I used mine as my suburban daily driver for a year!
You won't have to "un-hook everything" if you don't hook up everything in the first place. Your RV will come with tanks for fresh water as well as waste: To stay mobile, use those and only "hook up" for a few minutes to fill or empty as needed, every few days. Just plug in the electric, and maybe not even that for an overnight. Enjoy!
Non-macerator setups are more common. As one company rep stated firmly but cheerfully in a video I watched recently: "Gravity always works." Features like macerators and electric steps set off my "KISS Principle" alarms.
When I'm just getting from Point A to Point B, finding a campground for the night is a hassle, as well as an expense. Compared to a typical campground, Walmarts are :
Easier to find and access
Always level, pull-through parking
Always answer their phone
Better camp store
Better security personnel
Cleaner bathrooms (though not as well-equipped)
No check-in, nosy neighbors, kids running around, smoky campfires, or loud singing into the night
I'll typically head out early in the AM, do touristy stuff mid-day, then finish the day's mileage quota later, on my way to the next WM. Living in the northeast corner of the country, I often have to travel a couple of days just to get the "real trip" started!