Blue tank: we carried one the first eight or nine months we were full time... never used it. Sold it to a young couple at FT Polk while we were there.
Mail forwarding: what have you done about domicile? If you haven't taken care of that yet, a month isn't much lead time. We use the Escapees' mail service. The Escapees RV Club is based in Livingston, TX, and offers domicile, mail, and other services (they also have mail services based in Florida now). Their web site has a wealth of information on legal domicile and you can read about their mail service at:
Escapees LinkRob