Make sure you have a well fitting net to close off the cabin and keep the sandflies out!
I spend 15 to 20 days a year on Manapouri, it's a beautiful lake with plenty of sheltered spots but can cut up rough.
The public ramp is quite steep and there is not much room to rig and park. The boat club ramp further down the river is better but quite expensive for casual use at, I think, $25 to launch and $10 per day to park.