At least two of us have posted (or are in the process of posting) long narrative poems.
We have William Haskins'
Thorn Forest, which is finished and quite wonderful.
And I'm in the process of writing one called
Adrift on a Wine-Dark Sea (loosely inspired by the Odyssey, as I note in my signature, though it is definitely not a straight retelling). As William did his, I'm attempting to post mine section by section as I complete it. I've posted five sections so far; the sixth will come soon.
ETA:
Tips? Hmm. I think this depends on how you work as a poet.
I didn't do a formal outline of mine, but I did know before starting out what my characters would be like and where I wanted to go with them. I also knew the large metaphors and symbolism I wanted to work into the poem, and had a clear sense of how the sections would proceed and roughly what they would include. I also had a good idea of the general tone and structure.
If you are going to share it as an in-progress poem, as William did and as I'm doing, then I think it is probably important you have some idea of most of that stuff up front; otherwise, the poem may lack coherence. If you don't plan to share it until it is finished, it's less important because you can change your mind and revise the earlier sections. I must say I'm finding it extremely challenging to do it as an in-progress poem, since I usually write the endings of my poems first and work backwards!