The easy way is to convert the rust and get rid of any scaly or flaking rust use a wire wheel or cut it out then you can patch it with some new metal and use aluminum body filler by USC all metal body filler.
I used it extensively on my 04 WJ and it works great, I used in conjunction with the self adhesive formable stainless steel sheets you can get from any Auto Zone and put it over them, no welding involved. It doesn’t shrink or crack and you can drill and tap it. I have had Zero rust comeback where I used it.
You do have to follow the direction’s as the drying time is very short and ensure you put the lid back on after you remove your required amount as the air starts it’s conversion easily. I found out that by putting a little less hardener it gives you more time to work with it and it’s easier to finish. The first time used it I had to use a grinder to smooth it down as it hardens to a metal (aluminum) surface. Then put the your wheel flares back on.
