Was trying to install on Xubuntu 18.04. Kept getting error messages. Finally gave up and switched to Kubuntu 18.04. Kubuntu uses a different apt package installer ( the QApt Package Installer). It stated that Rstudio needed 10 additional packages and I clicked OK and it worked! It might be that one can install the QApt package installer on Xubuntu and it would work. I had tried both the software manager and gdebi on Xubuntu
If I get frustrated with Kubuntu, I will try to reinstall Xubuntu and Qapt package installer and report back.