Be very careful when you cut the hole, probably the most critical step. Wires can be anywhere in the walls, just because there is not a switch or plug in socket in the area does not mean there is not any wires.
Plumbing it will be your hardest part due to a very small work space.
How do you use your TT? putting an outside shower could give you a freezing spot and break lines, so insulate and build in a drain point.
My TT came with one, I never used it and bypassed it.
2014 Arctic Fox 30U
2001 Silverado 2500 HD, 4WD
8.1 Vortec / 4.10 gears / ATS Stage 2 Allison Transmission with Co-Pilot
Tekonsha Prodigy P2 Brake Controller
Reece Class 5 Hitch with 1700lb bars