There is a maintenance chart in the Keystone Owner's Manual. Why you didn't find it is ????? Check the 2019 version of the Keystone Owner's Manual, page 84. If you don't have a copy of the owner's manual, you can download it here: https://www.keystonerv.com/owners/owners-manuals/
That chart, by the way, sets the requirement to inspect and reseal the roof every 6 months. There is a comment on page 83 that reads:
"Inspect the roof at least every 90 days, paying close attention to all seams and/or joints and attachments where sealant is used. Look for cracks, shrinkage and/or gaps/voids in the sealants. These must be carefully cleaned and resealed. It is necessary to use the same sealant as originally installed if touching up cracks, shrinkage and gaps/voids. There is no way to know if 2 different brands of sealant will seal to each other. DO NOT use any type of silicone product on the rubber roof material
Note: The bolded, red emphasis was included by me, it is not that way in the manual, although I did not change the wording.