You get points for creative thinking.
I keep a log of every mile and every gallon of fuel on my truck, in a spreadsheet. Use the same spreadsheet to record replacement part numbers, repair costs, what brand of fuel, etc. So when I log that, I also log estimated miles in a trailer spreadsheet, and also include where we camped, nights camped, site numbers, and also repairs and part numbers. Since my entries are done at the same time as the truck, I don't forget.
Even though I do all that, and it is interesting, there are zero trailer maintenance items based on mileage.