I'm no rocket scientist but I do believe that the front cap takes quite a force from the wind pressure going down the road a @ 60mph.
So, with a ladder , properly padded, I use pool noodles cut and tapped on, your "full weight" is not resting on the cap.
Only a portion of your weight will be putting some pressure onto the cap.
Ideally .... the broader you can make the padded area that will be resting against the rv...all the better.
If you don't believe me do this little test ....Use caution and only at your own discretion ...to see how much pressure from your weight is put on a wall (or cap) ...lean the ladder against a wall, go up the average distance you would if on your rv cap, holding the ladder rung in front of you with one hand -- now push out slowly from the wall with the other hand...lifting the ladder "slightly" off the wall...notice that it really did not take a whole lot and certainly not your whole body weight.
IMHO... "most convex caps" should be able to support a reasonable amount of weight.
However, I have met some RVer's that think the front caps are paper thin and choose to treat them like a flower petal .
~ Just my 2 cents ~
'07 WildCat 30 RLBS ~ West Coast Edition ~
Trail Air - Tri Glide Pin Box
2000 F350 DRW 7.3 Diesel Lariat 89k miles
Edge programmer, 4" SS exhaust turbo/back
Vancouver Island, B.C., Canada