The cheapest route is to do open heart/roof surgery on it. My son had a TT with rotted wood around the ac unit and was quoted $5300. He didn't care about making it perfect, he just wanted to nurse it along. We removed the front trim piece and made a cut from the front back to the ac unit and laid it to the sides. We cut out the damaged area which was about 1/2 a sheet of plywood, added some filler at the seams and reinforced the area around the ac unit. We then glued the tpo back down and stapled the cut and applied dicor to everything. That was 3 years ago and it's been fine. The same place that quoted a full repair would have done the same patch job for $3,000 but we did it for less than $200.
If you are not in a position to spend a lot of money or the rig isn't worth it as his wasn't, just patch it up and seal it well. Anyone who walks by will never know the difference. Dicor is like a miracle drug.
His tpo was felt backed so it was a bit of a pita to remove but just go slowly with whatever you have and keep peeling. We did poke a couple holes in it while removing but just cover them with dicor. Like an old guy I worked with long ago always said.....in a hundred years who will know the difference.