Just wondering if anyone has any recommendations for a decent rust convertor?
I'd like to coat the front subframe on my FF before undersealing it.
I'll also need to treat the scab on my passenger side rear arch before painting.

Waxoil has a rust inhibitor in it & I have treated every car that I have owned & have never had any corrosion probs in 20 years of driving  Worse things happen at sea! Well thats what swmbo said when WRENS came to sea!!!

If you can find it Loctite 7500, the non industrial version is 'Rust Remedy' available from most motor factors.
Brush off loose rust, two coats and when it's turned black you know it's done it's stuff. It can be painted over after 24 hours as it acts a primer for most paints.
Bear in mind in this cold weather it will take longer to do it's stuff.

I painted a seriously flaky, totally rusty steel block a few years ago with two coats of 7500 and nothing else on top and it's been left outside since. It's only showing some minor rust spots on it now, with a top coat of paint I'm sure it would have been fine.

I use Kurust, sounds like it does the same as "Rust Remedy" above. Preparation is important, remove all loose rust and paint, sand down or wire brush on a drill back to good metal then apply the inhibitor/fixer. Then let it do its stuff, then prime and paint, and/or waxoyl. .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

Cheers guys. Would it be ok to spray it on?
I had heard similar good things about feretan also?

My advice is if you live north of the border get your underside Waxoil'd ASAP.

Every Scottish car I have bought has worse surface rust than southern cars. I guess its salt on the roads and the colder wetter weather.

Surprisingly cold (<4C) stops rust forming but I would agree with the salt and wet problem.
If you want a substantially rust free car buy inland as near the south coast as possible.

It's definitely the salt guys.
Hopefully get her treated next week.

Just done all mine with worth rust convertor in a spray bottle it's water based drys gloss black. Then mixed one tin of shuts with 4 parts wazoo and coated the full underside ready for MOT next month