You need supplemental braking to
comply with the laws of physics (more weight needs more retardation force...) and also to comply with the laws in most states. Some states like Oregon don't list a max towed weight above which you need brakes, but do require the combination to stop within a certain distance -- and this means brakes for your toad in nearly every imaginable circumstance...
Here is a typical map of un-braked trailer weight thresholds for the various states:
http://www.readybrake.com/state-towing-laws.html
Which states are you presently towing in so I can avoid meeting you there on the highway???
Chuck