I don't, cause I'm too heavy for the ones which are available. But if you are only 200 lbs or so, you can get one which collapses side to side (if you have a long, skinny place for it) or one which collapses top to bottom (short, wide, storage place).
Of course, if you have a ladder attached to the rear of the RV, its questionable why you need one. The built in will get you to the roof, and anything else, you probably won't need to get to until you get home (unless this IS your home, and then see the first paragraph).
I have a ladder attached to the rear of my Class A. I still carry a small folding type step stool with two steps to at least get to the top of the windows to wash them. I keep it in outside basement storage areas until needed. I thought of carrying a 5 or 6 foot step ladder which I would carry on the ladder in the rear (behind the bike rack or between the bikes and the perm ladder) or on the roof, tied down real good. I'm not a full timer (except for winter months), so until I can't reach the top of the outside windows with my small folding step stool (which gets me up about 30 inches off the ground) I won't take a large ladder with me. :laugh:
I carry an 8' fiberglass step ladder with me. I made up a bag out of nylon material, sewed it myself, that slides over the ladder. Then I strap it to the luggage rack of my tow vehicle. (I have a rack on the fiberglass cap of my Sonoma P/U) I like to be able to keep my motorhome waxed and clean. A lot of times I will get the ladder out and use some spray detailing wax to do the end caps. Seems they take the most beating from suns rays. I also use it to keep the windows clean.
The access ladder on my rig has a first rung about 5 ft off the ground. I carry a two step stool so that I can get up to it. I wash the rubber roof of the rig at least twice a year with Murphy's Oil Soap and a nice scrub brush. That also gives me a chance to check for any cracks on the sealants.
So to answer your question. Yea, there are people who carry ladders with them. There are some nice folding ladders out there now but they are expensive and aluminum. Never cared for aluminum ladders.
We carry a collapsable ladder, 8' long and folded it is about 5" square. We found it at Camping World, but other RV stores also sell them. By using this one we are able to keep it inside of one of our storage bays as my wife doesn't like things hanging outside on our roof ladder.