Originally Posted by man pkg_add

The environment variable PACKAGEROOT specifies an alternate location for
pkg_add to fetch from. The fetch URL is built using this environment
variable and the automatic directory logic that pkg_add uses when the -r
option is invoked. An example setting would be "ftp://ftp3.FreeBSD.org".

The environment variable PACKAGESITE specifies an alternate location for
pkg_add to fetch from. This variable subverts the automatic directory
logic that pkg_add uses when the -r option is invoked. Thus it should be
a complete URL to the remote package file(s).