Fuel tank caps was not modelled on all cars in LFS. Those are the part of car body and most of skins are far from being alternative. Thus, I hope this feature will be implemented in LFS. Maybe the gas caps would be opened while pitstopping, and closed after pit exit.
On the other hand, race direction will bring about a turmoil. Left/right one sided gas caps should be placed opposite side according to clockwise while pitting in reverse tracks.
Some related threads:
http://www.lfsforum.net/showthread.php?p=1034396#post1034396
http://www.lfsforum.net/showthread.php?p=656074#post656074
On the other hand, race direction will bring about a turmoil. Left/right one sided gas caps should be placed opposite side according to clockwise while pitting in reverse tracks.
Some related threads:
http://www.lfsforum.net/showthread.php?p=1034396#post1034396
http://www.lfsforum.net/showthread.php?p=656074#post656074