The Oasis dealerships, and others that specialize in DP's, have pits with various sliding platforms that they use to access the engine. Combined with the hatch open in motor homes you can get most of the needed work done.
There are some without the access and I can see it being quite a job.
Back when my alternator failed at 15k it took the technician all of 20 minutes to exchange it from the bottom using the pit.
No doubt FRED'S make a lot of sense regarding easier access.
Searching IRV2 might give the OP a feel for what others are or have paid.
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