You can always just use this command if your server is in 1.14:
/forceload add < 1stchunk > < 2ndchunk >
/forceload add <1stchunk> <2ndchunk>
justJust as if you were using /fill/fill, put the xzXZ of the first chunk location in the < 1stchunk ><1stchunk>, and put the xzXZ of the second chunk in the < 2ndchunk ><2ndchunk>. This will cause the specified chunks to always be loaded. Just be warned that this wont work if your server involves laggy things such as redstone, as if redstone is loaded in the lot, it will get very laggy.