If the mold is due to something that occurred after you purchased it, you could look into hiring a professional mold removal company to cleanup your RV. The Environmental Protection Agency has a terrific website on mold, including how cleanup should be addressed, at www.epa.gov. Given your health condition, you should consult with your doctor before you invest money in hiring a removal company, as to make sure that this is a viable option. Your doctor may say that no amount of cleanup will make the RV safe for you.
You said that this was a "new" RV that you purchased. It seems somewhat unusual for a brand new RV to have such a serious mold problem. If this mold problem existed before you bought it and this fact was not disclosed to you by the seller, you may want to think about consulting with an attorney in your area to find out if the seller violated any consumer protection laws. If the seller did break any of these laws, you may be able to void the sale and, perhaps, seek compensation for your illness.
You should also carefully read the insurance agreement you have on the RV. It is very common for insurance policies to exclude mold damage from coverage; however, it's still a good idea to check to see if this is covered in anyway by your insurance.
As far as your situation with the bank: If you simply stop paying them, then yes, they are likely to eventually take legal action against you to force payment. And yes, such action could negatively affect your credit for at least 7 years. After all, the bank is not responsible for mold damage, no matter when it occurred. They simply lent you the money, and will fully expect to get it back in accordance to the agreement you signed with them. By stopping your payments, you will be breaking the terms of your agreement, and will therefore be opening yourself up to whatever collection actions they are entitled to under your state's collection laws.
If the RV is indeed beyond repair and permanently unusable, and you can no longer can afford (or want to afford) paying the bank on this loan, you would be well advised to consult with a bankruptcy attorney in your area. A qualified attorney will be able to help you assess your situation, weighing the benefits of various options against the potential consequences. The laws governing loan agreements vary from state to state (and may also be affected by whether this RV was being used as a vehicle or a primary residency), so it would be prudent to have an attorney licensed in your state to assist you in this matter.
Hopefully, your doctor finds that a thorough and professional cleanup to be safe and viable option, so upon the mold's removal, you can continue using your RV. Or maybe you and your attorney will decide that there is a better option to be pursued.
Best of luck with this difficult situation, and I hope that the information I have provided helps you Find. Learn. Save.