Hello Edison,
As I have indicated from the post above, hosting the form externally is not the only solution. Option 3 allows you to add the JS code without having to host the form externally.
And there's no best option, since the code will either work with any of these options. It all depends on your personal preference and whether there are any other variables that can make one of the solutions more viable to implement than the other.
It sounds as if you haven't been successful in getting the JS to work with the checkbox. My recommendation for you would be to take the form code -- see step 3 from the previous response for the two options on how to do that, paste it in an external html editor in your computer, add the JS code, and then save that as an html page and troubleshoot the code and test it while it's on your computer. Once you get that page to work, you can then upload it to Eloqua and it will continue to work.
There are two ways to add JS to a landing page that was created using the awesome editor - a non-uploaded landing page:
1) The toolbox on the left palette of the landing page editor. From there, the last option allows you to add JS to the landing page.
2) The HTML static cloud component allows you to add any restricted code to the landing page.
Thanks,
Tarek