Actually no, if u use the proper paint, (ppg makes a good one), u will have no problems. See your local hot rod paint-supplier...i say hot rod b/c those type suppliers usually carry the "odd" type paints. i forget the number that u need, but a quality shop will know.
HOWEVER, that plastic renew does indeed work, but its directions must be followed exactly, meaning it is labor-intensive...my stuff usually looks ~85% as good as new...
I use a trickling water-hose and electric hand-sander (air sanders usually are too uncontrollable, making you get the plastic too hot, which will melt it---SUCKS...).
If you can befriend a local hot rod shop, they can be cajoled into blasting your tank with baking-soda, which will save tons of time.