You can also use the more informal "nakaikari a nabasa" which means "sincerely yours".
Here are other ways to express "truly yours" in Ilocano, depending on the context:
* "Kabayatan ti Dios" (With God's blessings)
* "Ad-duyngay a panagayat" (With true love)
* "Ad-duyngay a panagrespeto" (With true respect)
* "Ad-duyngay a panagballigi" (With true success)
The best way to choose the right phrase depends on the context of your letter or message.