For an RV filter, one like this will probably do OK. You may want to eventually beef-it-up but these are relatively inexpensive, can be used for one season, and tossed out if you don't like it.
Click here.Pressure regulator for your fresh water. If you are hooking up with a hose, it's always a good idea to use one. We had a hose explode on us once and the regulator was located at the campground spigot, not at the camper. The HOT summer heat caused it expand, weaken, and blow! Luckily, we were right there when it happened. Although you are on a seasonal site, when we have full hook-ups, we usually fill our fresh water tank and pump from there, just so we don't have the vulnerability of another hose breaking on us. You may want to store your hose away if you are not at the camper though for a few days, even if the water is shut off.
The water should be safe to drink, although it may be well water, or city water, or who knows. The water has to pass EPA regulations and board of health regulations as the campground has to follow those rules. Taste may be different than what your use to. That's where a filter is helpful. Even with that, many people bring bottled water. We don't .... if it hasn't killed me in 59 years, I think I'm OK. And even if it does kill me ... I've lived a good life!
😛Even if you hook-up your sewer permanently, you do not want to leave the camper valve open. You want to keep it closed and dump when the tank is full. Your gray water can remain open, but never the black. Dump only when it's full. If you don't, liquids will drain off and solids will pile up, and up, and up, and then turn hard! Flush the tank often.
As long as your sewer hose is sloping down hill, you don't really need any kind of sewer hose support. You can make-shift your own by getting a couple blocks and laying a board on them and then the sewer hose on top of that. It may look a little red-neck, but it words and if you have scrap lumber laying around, why spend money? Add a bit of paint to the board and it will work just fine. The important thing is to keep the hose slopping down hill.
Hope this helps ... others will chime in too with their thoughts. Consider all responses and then figure out what will work best for you. Good luck! happy camping! I'm glad you can still enjoy your camper even in the midst of some unexpected health and financial issues!