Hi,
because i couldnt get to run my ubuntu to activate coolbits, i bought ethos - well now so far i got it to work and mine, and its running good so far but i want to install teamviewer. Anyone done it? Or can tell me how? I already failed at “sudo apt install gdebi-core” 
ssh isn’t enough?
What error are you getting when trying to install? Is it just dependencies>?
I tried and failed a while back to get this to work. What did work for me was AnyDesk The Fast Remote Desktop Application – AnyDesk when using fglxr drivers - I no longer have the need to use this anymore so haven’t tested on latest version of ethOS and obviously they don’t recommend you do this anyway.
As to the ssh question - in my case I didn’t have ssh access due to firewall restrictions but obviously ssh is the preferred option.