I might confuse you cause I and terrible at explaining things but ....
To add to dude above, RG59 is the lower grade cable, RG6 is the choice for satellite. Its most likely RG6, I've havent seen RG59 really get used in RVs in awhile.
its probably going through a splitter like mine was from the factory. The line goes from the outside, to behind the tv, splits one to the satellite outlet and one to the tv cable/ant booster plate. (then its split after that to bedroom tvs/possibly FM radio .. etc)
if Dish is like Directv SWM (dont know cause I dont use Dish) it needs to be a dedicated line.
options ...
1) Remove the splitter, and theres a webpage
HERE floating around that instructs you to make your own jumper wire on the tv booster plate to grab the signal from the outside before it hits the booster.
some manufactures do this..
2) make seperate outside connection and run that to the satellite outlet.