An alternative to PL might be Loctite Powergrab. It's available at Lowe's, maybe HD as well. I don't have any experience using it on heat cables, but I've used it for a lot of other things and it works great.
http://www.lowes.com/pd_205801-133-1290020_0_?productId=3020319&Ntt=powergrab&Ntk=i_products&pl=1¤tURL=/pl__0__s?newSearch=true$Ntt=powergrab$y=0$x=0&spellCorrectedTerm=
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