My 2014 Prowler Lynx, a very much entry level unit, advertises "fully walkable roof" in their sales brochure. I would not walk, but slide on a 3/3-1/2 plywood to spread the weight. Am getting up there today for the first time to install vent covers.
I just knowingly bought a new 2014 Prowler Lynx 26lx which is low cost and below entry level (if possible) but it fits our needs for a camping utility of no more than 2-3 weeks a year mainly in the local area. I have had 3 Jaycos, 2 Fleetwood upgrade...