I don't think I would do that. Mine has a spring loaded roof cover on top of it anyway... As small as that roof area is surely you can find a way not to have to step up on the slide out roof...
I have the roof ladder on the end of my 5th wheel to get on the trailer roof and I have used the area between the slide and the rear of the trailer for a ladder support to work on the slide canves cover that really has never worked right from day one. Mine never draws up tight and flaps around when the wind blows...
Roy Ken