Change it myself, as I've done with every vehicle I've ever owned.
How to get rid of 18 quarts of oil? Geez, issues like that remind me of yet one more reason I prefer my gasser MH, and the fact it only uses 8 quarts of oil for changes. Which, easily goes in the portable oil container I use for all oil changes. Very easy to carry it to the auto parts store when going there for other things and dump the oil there (most take/recycle it for free).
Given how difficult I've found it to get ANY kind of RV related service done, I cannot imagine how difficult it would be if you had to rely on a shop to do all your oil changes. Mobile mechanic would be the way to go, if you could find a good one that would do it.