Water and Land Vehicles are tool profiencies as well.
That's right my Warforged Envoy can have a Galleon or Chariot as a tool!
Okay if the restrict that to the cheapest options a Rowboat and Cart, that wouldn't be over powered, those are cheap and not too big. Maybe the Warforged can act as a flotation/raft device and use it's arms as ors, and the land vehicle can have an extendable storage compartment, and roller skates on it's feet (so animals can pull him or her).
I still stand by my idea of a Warforged from the Last War who transforms into a small boat to fjord marines across rivers behind enemy lines and then join them in battle (without having any cumbersome craft for them to either carry around or have to stow somewhere where it can be discovered) and am determined to now play this character (probably with Ranger or Scout Rogue levels).