First off you do not replace the vent lid you put this cover over it...
next at 260 if you walk softly it should be OK but I would look at taking up a 3X8' sheet of plywood to distribute your weight over a greater area.. and becarefull with your tools up there rubber roofs puncture easily.
2004 Chev Silverado Duramax optioned past the max. 2009 Jayco Eagle 308 RLS 765 watts of solar, 6-6 volt batteries (696 amp hour), 2000 watt (4000 surge) whole house inverter.
140 days boondocking in 2016
211/2015, 196/14, 247/13, 193/12