We just purchased a 21SS Roo and one of the first things I did was slap some cameras on it. I found a little 7" quad-channel monitor and bought 4 small cameras (because I'm a gadget nerd and my middle name is Overkill).
I mounted one of the cameras on the tail gate of the truck for backing up to the hitch. #2 went on the back of the roo to see what's directly behind me. #3 and #4 each went just below the level of the frame of the camper, a few feet in front of the tires and look out at an angle so that I can see the blind side when turning in reverse.
I wanted them to be "always on" (rather than coming on only when in reverse) so I powered it all from the 12v aux/charging feed on the 7-way connector... I tapped in behind the socket on the truck for the tailgate cam and monitor, and inside the junction box where the Roo's power cable terminates for the 3 cameras on the trailer.
I had to make some brackets to hold the cams on the trailer... Some tinkering with metal for the two side cams and I wound up using mostly PVC pipe (in an L shape) for the camera at the back of the trailer. I attach it to the spare tire bracket with a C-clamp and the spare tire hides/shelters most of the bracket. Made them all to where I can pretty quickly disconnect them for when the trailer is in storage.
As for practicality... So so... The tailgate cam is awesome and I can land the ball under the hitch perfectly on the first try now (and for me, that is saying a lot). The two side cameras are pretty good... Can definitely see cars beside the trailer when traveling and where the tires are situated in relation to objects on the ground like the stripes on the road and close obsticals when backing up. The camera behind the trailer (which is the one I really wanted in the first place) is a little disappointing. The ones I wound up with are really wide angle, so there is practically no depth of field. Things have to be really close for them to be visible, much like looking in a convex mirror. Still better than nothing, but I might poke around for something that isn't quite as wide for that cam since I can see down the sides pretty well with the other two (and those "mirror" thingies on the sides of the truck
The 4-channel monitor lets me have all of these views at the same time if I want, or toggle to a single full-screen view or a split 2-cam view (for any of the cameras).
In response to the original question, I found plenty of places to tie-wrap the cables to the frame of the trailer. I put them all in split-loom on both the trailer and the truck to help protect them. I mounted mine relatively low because I didn't see a very clean (easy) way to get up high on the trailer.
I don't have any pics at the moment, but will take some in the next few days if there's any interest. Not sure if links to the hardware are allowed here, but I'll share if so.
Anyway, it was a fun project (even if I did get a little carried away).