I've done the Oregon Trail, the Continental Railroad, the Continental Divide and quite a bit of the Lewis and Clark trail. Not from any RV, but from my BMW Dakar motorcycle. I use the RV for staging and then head out for a week, come back, move RV and go again. IMO just about any of these trails, if you are actually following the real trail itself and not the highways with the markers, won't be any fun in an RV. For example; there are sections of the Oregon trail with rock mounds along it. The mounds are maybe 10 or so per mile. Took a little while to figure out, but they were graves. Yup; 10 graves per mile along that trail. We probably wouldn't have recognized the mounds as anything from behind a windshield, too busy staying on the road and not looking, stopping, etc...
Here is an example of a ride report. It's do-able in an RV I think. Just skim the photos and if that doesn't peak your interest enough to read the report, nothing lost.
http://advrider.com/forums/showthread.php?t=722112&highlight=OregonFor more rides and potential RV routes, look through these reports;
http://advrider.com/forums/forumdisplay.php?f=2Use the 'search' feature to search for reports that might interest you. By state for example. Or a river you like. Search 'Oregon' and get the reports on that state.