Welcome Dawn and Gary!
I can't help you much with your water heater question, but replacement Atwood models are fairly inexpensive if you shop around. It's a hard thing to eliminate since it uses such a big hole in the wall. You can even get them with electric if you want. What's the reason you want to go tankless?
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR