Suburban and Atwood are completely different sizes for same capacity
Suburban for Suburban
Atwood for Atwood
Otherwise you will have to do modifications
Anode rod should be checked at least 2X a year and replaced when 75% has been consumed.
Tank needs a good flush rinse and wouldn't hurt to pull and replace electric element as it doesn't sound like water heater was properly cared for in past.
Element is inexpensive and with it an anode rod out you can really flush inside of tank clean.....just remember tank has a glass lining so DON'T go scraping/gouging around inside tank