You do not have to replace all four if you don't camp where there is no power. If you always have power just replace two batteries after you remove the four old ones.
Take pictures of how the cables are connected up before you start so you won't have any problems connecting things back up.
2000 Sea Breeze F53 V10 - CR-V Toad
Some RV batteries live a long and useful life, some are murdered. Get a Digital Multimeter and Learn How to Use It