Temporary Rust Protection

I'm looking at buying a car that has been mostly sanded down to bare metal and wondering what is the best option to slow down any rusting over the next year or so before I get round to sorting out the bodywork properly. 
Ideally it should be something fairly easy to sand back off as a couple of panels have a fair bit of bondo that I'll need to address when I go through it properly. Would prefer something I can roll or brush on as I don't really have anywhere suitable to spray it. 
The car will have to live outside but I'm in So Cal so the weather is pretty good.

Spray can paint sands off easily

A lot of people who run bare metal cars use Gibbs Protectant, it's supposed to be very good.  https://gibbsbrandlubricant.com

I believe this would be a good application for Phosphoric Acid.

I buy it at one of the local stores.  They carry the Klean Strip brand "Prep and Etch."

I use it mostly to help try to stop rust that is already present...but I remember watching a youtube video that did an experiment and found it was a pretty good way to protect/store bare metal for a while if necessary.  A year might be pushing it (I'd prepare to do more than one application if it's going to be that long) and I'm thinking it might work well for storage...not so much a project that is actually being driven.

I use rattle can clear coat.

Thanks, this will hopefully be a driving project so maybe rattle canning it all one color would be the best bet.

Best option in my opinion would be epoxy primer. It will protect and not have to be sanded off except where repairs are to be made. Eastwood makes a roll-on version if spraying is not an option.

In reply to NOHOME :

Primer has to be covered with a layer of paint if it will be exposed to the elements, no?

Ospho and the cheapest spray enamel you can find. 

+1 for epoxy  primer. It will hold up and will not absorb moisture.