We had a diabetic dog we just helped go over the rainbow bridge after 13 years, last 7 as a diabetic. She went with us all over the country. We visited MANY vets over the years with one crisis or another. We always felt the issues would have happened at home.
We boondock for long stretches in Quartzsite. Vet care is a far distance away - best is to Yuma 70 miles away. There is only a part time local vet who is semi retired and another in Blythe who is good but they are SO busy.
Insulin she used is for humans and so could be gotten at a regular Pharmacy. We chose Walgrens as they are most everywhere we need on the west coast.
Find out about getting insulin and syringes while on the road(RX from Dr at some national drugstore chain!) You will need a consistent means of refrigeration for the insulin.
We loved our little girl and took the best care of her that we could. She loved to RV and we will miss her when we head out for travel this fall. She would NOT have done well with someone else but that was her.
Illness/inability to travel will eventually happen to us all. I encourage you to do what you can while you can. Maybe just not too far from medical for both of you if that is a need. May you have safe and joy filled travels.