I just went through the learning curve on this. I don't think RV facilities will work for a boat as their tanks are gravity drained, however I have not tried to use one so who knows. The Marine pump outs are plentiful and easy enough to use around here.
First thing you need to do- call the marinas at the waterways where you plan on boating, ask where the nearest pump out station is. If the person who answers does not know, ask for someone who does. If your pump out head is in good shape, there is no reason to remove or change it. There are pump out stations that are free at both Long Beach and Los Alamitos harbors (not sure where you are but hey someone reading might like to know).
Second- go to your local Walmart and check out what they carry. I went, expecting to find one type of RV treatment, and found an ENTIRE AISLE of products. There will be so many it will be overwhelming. Find a good one in your budget and get some of the RV-friendly toilet paper too. If you can get one that has formaldehyde, I recommend it, because those keep the odors at bay better. I just googled rv treatment reviews and picked one. I use the little powder packs that dissolve rather than a liquid because a bottle of liquid can spill or dry out.
I keep a gallon jug of fresh water just for filling the head in my boat (I have a raw water intake but it doesn't work) but also DO NOT put saltwater in your head. It makes an awful odor. I can get about four flushes with one gallon. You will learn with practice how to use a little water as possible to flush. Lake or river water is fine to fill the bowl if you are not in the ocean.
Never put regular TP or feminine products down the head.
Always keep a gallon of water in the holding tank with one dose of treatment at the minimum, otherwise if any solids are in it, and it dries out, you will have issues.You will want to have it treated before you need to use it.
Don't use bleach to kill odors in the tank, the treatments use live enzymes and the bleach kills them, sending you back to square one. The enzymes break down the solids and RV toilet paper into a liquid that can be pumped out.
My boat is 43 years old and the head functions great, does not smell and is easy to use and maintain. My wife and daughter are very happy its there.