Rust - Rust proofing frames, Rusting treatment and prevention

I have a steel frame that i'm re-conditioning.
On the top tube there's areas of rust damage that i want to clear up - it's not gone through the tubes at all, just pitted the surface, and only revealed itself after sand blasting.
I'm thinking of using something like 'liquid metal' or car body repair filler and then sanding it down smooth.

Any recommendations on best products/approach - i assume whatever i do is going to have implications on how it gets repainted.
eg filler won't powdercoat, will any filler be suitable for stove enamalling etc etc

Thanks

Jim