Don't brake so hard?
Seriously though, the best way to stop it moving forwards is to take a second rope form the bow eye back under the boat to something solid on the trailer chassis.
Problem with strapping ribs down with the traditional strap over the back is that the tubes will never be solid enough to actually hold it down, even with the biggest ratchet you can find. You would be amazed just how little slack a strap or needs for the bouncing to move it to a place where it's even slacker.....
So, Rope from your bow eye aft to the chassis, and a strap (or two) to a solid point on your transom to stop the stern bouncing. (most have U- bolts handily placed for this)
It;s the unfortunate thing with roller trialers - the frictionless ease of launch & recovery becomes it;s own worst enemy on the road!