If it's just a bit of surface rust, waxoyl or similar should sort it - use a hairdryer to warm the frame tubes and make sure it gets to the extremities. Bob Jackson recommend Dinitrol ML, which comes in an aerosol; you can get an extension hose which makes it easy to get into all the nooks and crannies. Both Waxoyl and Dinitrol seem popular with Land-Rover enthusiasts, so they are both presumably fairly tenacious.
According to the Dinitrol can it treats existing corrosion and delays its progress; AFAIK Waxoyl is also full of corrosion inhibitors. I wouldn't rely on them to treat really heavy patches, but if it's just the normal orange surface dusting you get in a frame it should be fine.
If it's just a bit of surface rust, waxoyl or similar should sort it - use a hairdryer to warm the frame tubes and make sure it gets to the extremities. Bob Jackson recommend Dinitrol ML, which comes in an aerosol; you can get an extension hose which makes it easy to get into all the nooks and crannies. Both Waxoyl and Dinitrol seem popular with Land-Rover enthusiasts, so they are both presumably fairly tenacious.