I wish I had an answer to that question that included a suggestion for inexpensive and reliable coverage, but I don't. The same options are available for RVers that are available to non-RVers.
Some employers provide health insurance coverage for their employees.
The self-employed, and employees who don t receive health insurance as an employee benefit, can usually buy individual or family coverage directly from a health insurance agent. Group coverage through a professional or social organization is also an option. The cost is dependent on numerous things. For individual policies, the age, weight, medical history, occupation, and leisure activities of the insured are major considerations. Other factors are the types of coverage included, the deductible, the amount of co-insurance, and the total maximum payout limits of the policy.