The rust converter mentioned is phosphoric acid, comes in many flavors. Body shops sell one brand, marine stores have a brand named Osphocote (I believe). Just look for a product whose active ingredient is phosphoric acid.

Phosphoric acid converts iron oxide (rust) into another compound, whose name escapes me at the moment, rendering it rust proof and stopping the cancer of rust. The most likely reason your paint flaked is because a good painter will treat a bare frame with a phospho acid etch before painting. Yours didn't.