If no food touches it, does it need to be toveled (immersed in mikvah)?
Here's what R' Aaron Felder has in Oholei Yeshurun, Vol. 1, Chapter 3: "Laws of Tevilas Keilim", Section 5: "Utensils Not Requiring Tevilah":
Here's my translation of Footnote 124, which is in Hebrew:
The cited section of Shulchan Aruch gives an example of some vessel that one puts pots on, which therefore does not need to be dipped; and another vessel that one puts food directly on, which therefore does need dipping.
According to R' Felder's bibliography, the book Tevilat Keilim is by a R' Tzvi Cohen of Bnei Brak. I don't know who he is or how authoritative his ruling is, other than that he's quoted a lot in R' Felder's footnotes. His point may cover your situation, since most people don't line their pots.
Anyway, are you really going to only ever use the pot with a liner? If you're ever going to put the food right in it, I think it'll need to be dipped.
Please note that while R' Felder is a talented and respected Posek who cites an impressive collection of sources, his is by no means the last word on the subject. If this issue affects you practically, you should consult your Rabbi, especially since your situation may very well be both a borderline case and the subject of dispute between authorities.