anything better than nothing!
You should put something on for protection against further damage--and soon!--you could use a rust converter like "Extend"by Duro,a company owned by Permatex,or "Rust Reformer" by Rustoleum,you can get both at Home Depot or most department stores-"Rust -Mort" by SEM works good too,but only body shop supply stores carry it..
-I use Rustoleum paint for temporary protection until I can do the job right by sandblasting,and primer,paint etc.Actually,it holds up pretty well--I use the brush on stuff,it goes far and the thicker application prevents re-rusting longer--the spray bombs work ok too,but dont seem to have as much rust resistance in my experience--and the liquid used to be better before the new formula "low volatility" stuff came about--if you find some old stock in a store,its better stuff than the new variety..Regular automotive enamel can be used too,but its not very brush friendly--spray gun works best...
Or you can use POR-15,a rust converting paint--but its pricey at 22 bucks a pint,and rather difficult to find locally--it also fades to flat black if exposed to sunlight--and other paints dont adhere well to it unless applied when its still tacky..nothing beats it for durability though,but I prefer to use it under the vehicle on the frame and underbody panels more than on the outside...
Anything is better than nothing!--on my van,I tired of having to paint the roof every 1-2 years,so I tried Mobile Home Aluminum Roof Coating,its been on 8 years now,and its finally needing to be done again!--its not pretty,but its kept the rust away a lot longer than any paint I used.(its cooler inside in the summer too!)..I'd rather have an ugly truck than one with rust holes,and have to "bondo" it back together..
