I like sean's design where you just level a base and its riding on a few stakes.
MY spiral megatree is a similar design where I just mount the base on 4-5 big stakes and level it. Then the tree sets on the level base. Its been very easy and it's always on a steep side of my neighbors year.
IN the past 4-5 years, on a traditional 18' megatree ... I didn't run the megatree down to the ground anyways, and used a PVC hoop on the bottom of the tree ... so being in a swale hasn't mattered much. The strings of lights (once attached to the base ring) will largely support the bottom ring ... and it can hang off the ground as much as needed for your grade. I then stake that bottom hoop with some rebar and bungies and it stays put ... or doesn't swing around in the wind. I found the cheap dollar store bungies worked nice to attached the super strings to the hoop and as the string slacked a bit, the kept everything snug.
One big thing, esp. if you using new strings of lights is to get the twists out and stretch them in the sun for a day to remove the slack before hanging. Once they have done this, they will hang with less slack change after hanging and attaching. You can also let them hang for a few hours if the weather and wind permits.