As Bob mentioned the roof.
Many RV Extended Service Plans (also referred to as extended warranties) require that the roof be inspected on an annual or other time sensitive basis. Read your extended service plan and highlight any gotchas that may be in the contract.
If you perform services yourself you need to document when the services are performed, what was performed and maintain receipts.
RV Life has come out with a cloud based subscription service app that I am taking a look at. It does cost but so far I like the features. One downside one thing I addressed with them is tracking DEF usage and although I didn't like their recommended solution I came up with a method that fits my needs.
The photo is the dash board when entering the system and the attached document is my maintenance schedule so far. I have not entered all of the equipment so it has not listed all of the maintenance required. For some items they have the maintenance requirements but for others you have to set the maintenance schedule.