With a tri axel there should be no issues at all whats more important is make sure your tow bar is set at the hight so your towing nose up/down and just always try & load up even make sure your loads strapped on nice and your tyres are all pumped up even and you should be fine
Good luck
Regarding tow ball height, that's why I wrote check recommended height and adjust hitch to suit. Regarding axle loads I simply meant that with towball at correct height trailer will be horizontal, so all will be doing their share.