Sorry Page Content Question.

You can use iFile too, but, I think you want something like this:

when RULE_INIT {
    set ::background BACKGROUNDBASE64HERE=
    set ::sorrypage  CONTENTOFBASE64HERE==
}

when HTTP_REQUEST {
    if { [active_members [LB::server pool]] < 1 } {
        if { [HTTP::uri] ends_with "background.jpg" } {
            HTTP::respond 200 content [b64decode $::background]
        } else {
            HTTP::respond 200 content [b64decode $::sorrypage]
        }
    }
}