Body Filler or "Bondo" is a good thing. This video explains why being afraid to use it can actually cause more problems than correctly applying what you need. Tools, materials & merch below:
*** Body Filler: http://autobodymaster.com/product_list.jsp?PHPRJ_GROUP_ID=1868 $21/gal
*** Metal Spreaders: https://www.jbtools.com/gl-enterprises-1101-coster-steel-auto-body-spreaders-3-steel-spreaders-4/?wi=off&utm_source=Google&utm_medium=cpc_a10-
*** Cheese Grater Blade: Stanley® 21-299, Surform 10" Half Round Blade Standard Cut
*** Small Rubber Block: https://www.harborfreight.com/4-78-in-soft-rubber-sanding-block-69574.html
*** Primer: https://www.myautovaluestore.com/autobody-master/lacquer-primer-abm-lpg1
*** Lacquer Thinner for Primer: Any brand lacquer thinner will work like this - https://www.homedepot.com/p/Klean-Strip-1-Gal-Lacquer-Thinner-GML170/100198758?source=shoppingads&locale=en-US&&mtc=Shopping