It depends exactly on where your power enters the HTT, and where your circuit box is located.
The easiest solution is to a twist lock style cord. Cut the cord a couple feet longer than the outside wall. Remove the old cover, install a new twistlock hardware, caulk and screw it in. Buy a new cord. FYI, it looks like you do have to modify the hole a little to get the kit to fit.
Otherwise, making assumption your cord and circuit box is in the same location as on my 23B, along the back wall. Remove the circuit box (disconnect the battery first), there are 4 screws holding the box in place, as I recall you have to remove the decorative trim. My HTT is in winter storage and I cannot access it
. The box is hard to remove at first, pull it out just a bit, and then you will need to reach in, mostly blind, and remove a screw that anchors the shore power cord to the floor. Once the cord is free, it is easy to pull the circuit panel box out. Then tie string/cord to the old power cord, pull it out, tie the string to the new cord and pull it back in (have help with this). Then put it all back together, make sure to reanchor the cord (but give yourself a little extra cord). I would think you could easily have ether option done in less than an hour.
Good Luck