This looks pretty promising
2300® VEHICLE BODY SEALANT
https://www.geocelusa.com/product/2300-vehicle-body-sealant/
and for the lower sections that have rotted
Clear Geocel GeoBond Instant Vehicle Roof Repair Kit
https://www.amazon.com/Geocel-GeoBond-Instant-Vehicle-Repair/dp/B0053GMDO2/?tag=ihco-20
2300® VEHICLE BODY SEALANT
https://www.geocelusa.com/product/2300-vehicle-body-sealant/
and for the lower sections that have rotted
Clear Geocel GeoBond Instant Vehicle Roof Repair Kit
https://www.amazon.com/Geocel-GeoBond-Instant-Vehicle-Repair/dp/B0053GMDO2/?tag=ihco-20