Hi @mknafl!
For packages hosted on CRAN, we provide a package cache mechanism for rstudio.cloud to help out with packages that require a lot of memory when building from source (keeping in mind that during this phase of our product we limit sessions to 1GB memory). Unfortunately, we do not have such a feature for bioconductor packages.
If the problem is related only to RcppEigen failing to build, it now appears to be cached for R 3.6.0 so please try to install again. If there is a bioconductor package that is failing on out-of-memory-like conditions, there isn't much help we can offer at this time. Perhaps you could try installing all of the dependent packages first, restart your session (to clear the memory utilization) and then install just the single bioconductor package that is problematic?
Good Luck!