I just checking in an RV today with 5876 miles on the trip! He picked my cross country mileage option so no charge as he was allotted 6000. Anyway you should consider a maintenance book (or spreadsheet) to make this a little easier. Obviously you’ll have oil changes but there’s things like a radiator flush, transmission fluid, etc. even tires have an expected mileage limit. These items are not as frequent as oil changes but if you make a running tally of what should be done at what increments then when it comes in all you do is knock out anything that your past the mileage for. You’ll want to group services that are close in miles and don’t sweat being over by a few hundred or even a couple thousand miles from a long trip return as these are just guidelines and there’s wiggle room on these big engines especially if well maintained.
luckily my guy that just checked in is a diesel with 20k recommended oil life so I still have no need to rush off to service.