Getting a Youtube channel's video list as an rss feed

How can I form requests using the youtube api to get the videos from a channel as an rss feed?

I read this question, where a link to the new api (V3) is given, but I couldn't find it there. I tried with the deprecated syntax from api v2:

https://gdata.youtube.com/feeds/users/UCqAEtEr0A0Eo2IVcuWBfB9g/uploads

but it only works sometimes.

I also tried:

https://www.googleapis.com/youtube/v3/search?key={your_key_here}&channelId={channel_id_here}&part=snippet,id&order=date&maxResults=20

where I enter the channel id and the search key, but I get a 'bad request' error.