The fact that you don’t have a permanent home should not affect your eligibility in State B as long as you are currently residing there and intend to remain there.
In HealthCare.gov states, you will be required to document your move. You will have to submit documents showing your former address (such as a lease, voter registration card, pay stub, or phone bill showing your old address). As for your new address, you can submit a signed statement to the Marketplace stating that you are living with your friend and you aren’t just visiting temporarily. Your friend will also have to submit documents, such as those described above, to prove their own residency.
Also, in HealthCare.gov states, to qualify for a special enrollment due to a permanent move, you must have had been enrolled in other minimum essential coverage, such as under a job-based health plan, another Marketplace plan, or Medicaid. You must have been enrolled in such coverage for at least one day during the 60-day period leading up to your move. There are exceptions to this rule for people moving from another country and for American Indians and Alaska Natives.
In addition, in HealthCare.gov states, the Marketplace will not make this special enrollment period available to you until you have actually moved.
Contact your state Marketplace for more information about the permanent move special enrollment period.