GM A-body Rear window rust repair

[SteveMcqueenRules]

thanks for all the info guys. I thought a stretcher shrinker would be perfect for this job but don't know if it would be wise to buy them for just this job.
The drain tubes is a great idea and one I thought about doing after putting a nice coating of POR-15 along the channel.
Here is a pic of the damage luckily it is constrained to just the areas covered by rubber and doesn't extend into more visible or harder to replace areas.