Welcome aboard 2fulltimers !
Similar challenge with DH's maintainence blood pressure meds. First year we stayed several months with relatives, who recommended a fabulous pharmacist in their small town. She did ALL the leg-work. Netted 6 months worth of meds, at a considerably better price than in southern California I might add. We eventually DID return for the winter, so a simple Dr. visit and blood test resolved perscriptions for another year.
I must note:
We've drastically simplified our medical lives: no insurance layer. Have been receiving incredible (50-70%) discounts by paying cash: meds, blood tests, physician visits, etc. Our once 'primary' physician expressed relief he didn't have to hassle with an insurance company to gain us enough meds to travel fulltime.
Have you folks identified a favorite RV park (s) where you'll spend couple months as basecamp or winterover site? Seek out a physician (or pharmacist) in those areas. Even insurance companies recognize folks move...and should (?) allow you to change your primary physician once in a while.
Hope this helps. Cheers!