I use a 625 with just one sattalite, I use a splitter (The one suggested by MOTOSAT, not the one that came with the receiver)
and a roof mounted (For the moment) Auto=in-motion-tracking Dish (Motosat) no special stuff other than that Dish-Network splitter (which you get for a Dish-Network sales distributor)
Here is what you need to know to set up a DISH 635 for a single sattalite
One, Choose your bird, Dish can tell you what channels are on which bird, The TV guide on 110 is only a few days long, the TV-Guide on 119 is much longer (weeks) but this is not normally a concern since you can program a "Search for shows by title" on a 635
Your "Super city" will need to be selected so as to make sure the one you pick is on the sattalite you pick (this is part of your RV declaration)
Now, comes to hooking up, Dish lead goes to the splitter, Pass through to receiver 1, other to receiver 2, Turn on. MENU-6-1-1 and in the option that shows 500, change it (The other option is 300) in the sattalite option enter the birid of chioce (110 or 119) and from there on it's easy (You should know how to do it if you have done it for a 500 dish)
It's that easy
Option 2: I have two dish antennas here, a 300 and a 500. I've yet to hook up, one of those will be hitting the road with me, just not yet sure which
(For when the signal to the T-2 Automotion on my roof sufferes from the microwave eating tree I'm parked under, IE: right now)