I have Express Scripts - though not thru Tricare. Been FT since 2018. For 90 day supplies it has just taken a bit of planning - to know where I will land and can receive mail. At a few places I can receive mail where I stay and at others I confirm ahead of time that a post office will take General Delivery (and how long will they hold a shipment - it varies). Express scripts lets you set up temporary addresses then to have the prescriptions sent to you. I did set those by phone not just thru the computer because, well you know, stuff happens. I took all prescriptions off of them shipping on an automatic schedule to make sure nothing went without my planning.
I do use a mail service thru a different RV group I belong to, but choose not to add to the number of handoffs and possibly delays - or extra postage charges - that would occur by sending my prescriptions thru the mail service.
I have prescription creams that do not work well as a "90 day supply" and for those I use Walmart and their ability to transfer the prescriptions
Safe Travels