On my 2006 jayco 29FBS, the external black power cord did a "transion" to an internal thick orange 110/120V cable. This transision was performed within an electrical round box. For my TT's 30A surge guard install, I simply removed this galvanized electric box, installed a wood mounting plate, then installed the 30A Surge Guard device. Clean and simple. re:
For your Jayco TT, follow its back external cable and see if it does a transion as well. Hopefully it does. And, you can replace the transiton junction box with your Surge Guard unit as well. Or, pehaps splicing into its existing black cable (inside the TT) might work as well...
Hope this helps.