I keep a Google Docs worksheet with the same information as everyone else:
Arrival Date
Departure Date
Campground
Site #
Site Notes
Who went
Camped with
"Camper stored before/left from"
Camper stored after
Miles towed to campground (2,143.4)
Miles towed on return (810.5)
Notes (Total miles towed: 2723.9) (excludes line 2 from pop-up)
# Nights (42)
Cost (644.23) / night (15.34)
I use an app for tracking milage in all of my vehicles.
And finally, I keep a worksheet for maintenance on the truck (again on Google Docs).
I do NOT keep a worksheet of mods or fixes for the camper itself. I just don't want to know.