There is a picture of extended valve handles and a discussion about them coming apart in this thread:
Here is company offering a 10"-12" extension kit:
They also offer cable operated valves if you don't have straight shot for rod.
My trailer has long (almost full width of coach) from the factory. The handle is threaded on, so all you need to do is unscrew the handle, add a piece of threaded rod, and screw the handle back on the piece of rod.
2004 Dodge Ram 2500 Club Cab 4x4 CTD
2007 Sunline Solaris T-276-SR: Misty Blue/Cherry
2001 Dodge Ram 1500 Reg Cab 4x4 OFF-ROAD