In reply to ianmurph:
One way would be to use a string, and keep adding/concat-ing to it.
module test();
logic [7:0] rx_message_array[];
initial begin
string s = "0x";
rx_message_array = new[4];
foreach(rx_message_array[i])
rx_message_array[i] = i;
foreach(rx_message_array[i])
s = $sformatf("%s%X", s, rx_message_array[i]);
$display("%s",s);
end
endmodule