I know that it's possible to make the payload cart go underwater. I don't see why it wouldn't be able to.

i don't know what you're doing but i need it now

http://tf2maps.net/

yes

If you can make a flying hover train that airshots the soldiers at mid I'd love you forever

make a penis shoot up into the air when mid gets capped

http://forums.tf2maps.net/showthread.php?t=13455

koth_windmilltrainsaw for esea s13

Ask clandestine about putting vehicles underwater