For anyone that hasn't heard of it, GacoRoof is - by far - the best roof sealer.
Developed in Seattle, it's 100% silicon!
This comes highly recommended by many RV'ers.
I used it on the roof seams of my 33 yr old Winnebago and it works great!
Be warned - it's NOT cheap - can run between $60-80 for a gallon can but worth every penny.....
well, that's my two bits..........
~Robert the Hair