I only masked when I treated the top the first time. Since that time I've used a cheap (not foam rubber) paintbrush and applied the treatment with that. It takes more chemical, but it's much more thorough and has no overspray.
There can be some dripping/runs, but that is easily cleaned up with no resultant problems. I just keep a rag in my pocket and if there's a run, I wipe it up (Usually literally - up, that is, since it's almost always on a side window.) immediately. I find that being careful at the edges reduces that need greatly. I open the top slightly to do the back edge.
I go over the top twice, and do that twice a season - spring and fall. I usually go through about three bottles of protectant a season. At least a full bottle each time.
I've used this method seven times now, with no problems at all. Until the fabric gets fully soaked, which is going to happen no matter what is used, it beads like it's waxed.
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Steve
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