I weight 240 and the tech where I purchased my trailer suggested I not trust the roof. He told me the ladder is only supposed to hold 200, and if I got on the roof, to stay on the edge.
I think he might have been a tad conservative, but Im not gonna push it. I would rather get on a stand alone ladder.
At 325, I would not trust either the ladder or the roof. Might work once, might work twice, but I think that's definately pushing it.
Just get a stand alone ladder and work from it. or maybe get some 2x4's to span the width to distribute your weight.
Mike