How to Vote
Because of how much lag constant base loading normally causes, FTBU chunk loading only works while you are online. In order to load your base while you are offline, you can vote for the server, which also grows the server. After you vote three times, your base will be loaded once the server restarts. It will remain loaded until it restarts 6 times, which is 24 hours later. You can vote every 24 hours to load your base.
Please note that only players with the member rank or higher can load chunks using FTBU, and by extension players with the guest rank cannot vote to load their chunks.
You can vote at all three of these websites to load your chunks for 24 hours.