Mufasa, Leave Behind or Take With Me in my RV

I came to stay with friends in ID last yr while filing for my disability, which I was awarded recently. While here I befriended a semi-feral spayed Female cat that had been left behind yrs ago by a previous renter. I've managed to tame her considerably. She likes food. I can pet & hold her. She seeks out love & affection from me. She sleeps on my bed. My friend says I should take her when I move. Mufasa only knows living free in farm country. I would LOVE to adopt her. I bought an RV. Mufasa Loves being in it. She wasn't thrilled when I started it up, but she did really well with the new experience. I'm leaving this area next month. I want Mufasa to come with me. I'm the Only emotional attachment Mufasa has besides Eddie, the dog. I'm her person. She is very content being inside. She is food motivated. Can I use that trait to solve the following: Mufasa will only go to the bathroom outside in the dirt in her "special spots". She'll hold her pee/poo all night & wait to go outside in the AM. I tried dirt from the yard in a litter box in the RV, no dice. If cats could laugh Mufasa would have when I showed it to her & tried to place her in it. What can I do to get an approximately 6 yr old cat who's lived outside her entire life to live indoors & use a litter box?? I just want to do right by Mufasa. The thought of her getting left here one renter after another kills me. I'm concerned she will be stressed in the RV. Food can only fix so much. Although I think she could get used to being confined. Its the litter box training that's got me really worried. PLEASE ADVISE
Cindy Montalbano
Rupert, ID