I used to use Proflex on sidewall penetrations, and it is good. But, I've been using OSI Quad for a while now and I think it stays cleaner, is more flexible, and is easier to apply than Proflex.
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch