We had a 2000 Itasca Horizon and needed to replace the heater core. Taking the spring clips off wasn't a problem, just keep track of them because they like to fly. I used a flat screwdriver to pry them off.
Once the case is split, the rest is relatively easy.
It also helps if you have 3 arms, each being 6í long. It's doable and you'll learn some new words.
By the way, somewhere in the world there is a 2000 Itasca Horizon with 2 of those little clips missing and it still worked fine.
Denny, Connie & Shadow (former barn cat made good)
2006 Tiffin Phaeton, Cat C7, Freightliner Chassis