I'm not sure what a quad bike/Vier Bike is.
125 lbs is not going to destroy the ladder.
Your camper has springs and shocks, so the "bouncing" will not be so harsh, no more than you climbing on the ladder and bouncing a little.
Is this a battery bike? Take the battery out to lower the weight.
Can you secure the bike such that the tires are touching the bumper so there is another point of contact?
You will find that forum people panic quite easily. Ask and they will tell you to never even climb on the ladder as it could break.
I have seen many ladders with multiple bikes and other junk on them.
Always a potential that the ladder breaks, but Im doubtful that the ladder will fall off on a trip all at once.
You should be fine.