Your system can leak for various reasons. Where the Hose lock connector connects to the tank at the top can leak and will if not already, at some point. It wont seal properly after a while and will secretly drip as its filling leaving water on top of the tank which will slide off as you drive around.
In fact any connector can leak including any Jubilee clips so just tighten them a little and put PTFE take around the Hose lock connectors.
Your Pre-filters can leak if you've changed them and they aren't nice and tight.
The RO unit can drip from the end if its not tightened up properly or its been so cold outside that the water freezes slightly and expands - it will drip as it fills and can be hard to spot unless its a torrent. If it drips, take the end off, pull the end part out, wipe the rubber seal and tube where its seated and put back together nice and tight, no more drip.