What is your RV filter specifications?
Does the RV filter remove all the minerals similar to reverse osmosis filter?
If yes, then you will have to add minerals(example GH+ salt) into the water as all fish need some minerals in the water.
Soft water fish (most South American and Asian fish) will require lower GH (estimation GH 3-8), and will need less minerals.
Hard water fish (most African fish, livebearer: Guppies, Mollies, Platies, Rainbow fish) will require higher GH(probably GH above 12), and will need more minerals.
1) Firstly, check what is your tap water GH?
2) Next, what fish do you want to keep - soft water or hard water fish?
3)If your tap water GH is suitable for the fish that you want to keep, then you don't need RV filter.
Otherwise, you will have to add minerals into your water after going through the RV filter, which mean higher cost and more testing of your water GH to ensure the water is suitable for your fish .
Also, you don't want to have GH swing if you don't add the minerals in the right ratio.
Please read the Information about GH below before deciding whether you want to use RV filter and what fish that you want to keep:
Beginners aquarium chemistry: water hardness (GH) This guide covers ideal GH levels, how to test, adjust, and more!
fishlab.com
This practical guide for beginners explains what these water chemistry terms mean, when you should test for them, and how to raise or lower them if needed.
www.aquariumcoop.com