So you mean can the trailer's converter bring those new Trojan 6s up to spec? Maybe, since most rigs have a converter that only does 14.4v or even only 13.6v, and Trojan wants charging at 14.8v. However, it is the best you can do unless you have another charger that will do higher voltages.
See what happens, and if the SG rises to Trojan specs then that voltage was enough and you are good to go. Don't forget to adjust the hydrometer reading for temperature so you know you got the SG up enough. SG spec is for 77F so if it is colder, electrolyte will be denser and the float will ride higher, giving a higher SG. False reading if you get to that spec SG when it is cold---you are not there yet!
If you have a lame converter that can't do Trojans properly, you might want to get one that can, but don't rush out just yet--see what yours can do first.