most etch primers are acid based and you can coat you bare steeel with this fin but you cannot go over it as it will not adhere properly and will caus more problems in the long run, best way to go is a epoxy primer which is a 2pac metal sealant/primer. this is designed to seal off any bare metal and give you a good substrate to start and bog/repair work on top of.
worst comes to worst, wait till ya saved up the cash and take it in to be done properly first itme, as if you decide to do bits and peices like this yourself then at a later stage take it to a shop to get painted ect it will all have to be removed and redone for the shop to provide any type of warrenty on the work
may help may not
http://www.gtrefinishers.co.nz