Install .deb or .rpm in gentoo

[Jian11231]

I understand the portage as the heart of the gentoo and I enjoy it while installing the package. However, some other package available only in .deb and .rpm only.
My question is how can I handle those file in gentoo. I'm had been look around the solution provided by other forum, but I'm apologize that I don't quite understand for those solution details.
The solution that I found as below:

1. Use the rpm2targz or deb2targz to convert it and cooperate with pkgtool.
Can some one show me the details how to use these package, because i didn't found any guideline for these two package.

3. Write the custom ebuild for the .deb and .rpm file.
Can someone guide me how to do this.

I'm apologize that I new to gentoo and don't familiar with those conventional rules in gentoo, I hope someone can give me the details guideline to these issue.

[Ionen]

There's a few ebuilds that install a binary-only .deb/.rpm in ::gentoo already.

Set the right RDEPEND it needs, use rpm.eclass or unpacker.eclass to unpack the .rpm or .deb, install files normally (in /opt if possible, but if hardcoded paths don't allow it system is fine too).

net-im/webex or plex-media-server for examples.

Not to say it's a very friendly approach if not already familiar with ebuilds, but it's easier than it looks if give it a bit of time.