Is the "bottom" of your RV enclosed? If so, you'll simply need to either drop the material covering the bottom, or cut holes in it, (not my recommendation) and trace the cable from the handle to the valve. Once you determine the length of cable you can purchase a replacement cable and install it to correct the problem.
Days camping (2016)----181 days
Days camping (2017) --- 82 days
2016 Wildcat MAXX 28RKX (33' TT), 2007 13' Scamp
2015 Ram Laramie Hemi, w/air suspension
30 years RV'ing
11 different RV's