Like the title says is there a easy way to fix rear 1/4 rust with out a lot of body filler?

 

Not really. The rust is ALWAYS further out behind the surface mess and just returns in a year without a doubt. It will corrupt your filler, also unpainted fill is like a sponge. Behind the repair, it will absorb moisture and fall out or swell up.
Fiberglass is the way to go but messy as hell and takes talent to get it right. The wrong temp and it will cure in your hands, the wrong mix and it won't cure on your car.
Good luck

 

Cut out rust and weld in new metal. Just did this to my this past labor day weekend. We cut the rust and from the inside we put the patch panel in to create a leap then welded, grinded, filler, poly flex glaze, then urethane high build primer. Then back on the inside I did the por15 treatment and used a seam sealer around the patch panel edges to seal it on the inside. I'll post pics of the repair later

 

The correct way is not fiberglass, and its not that hard to work with, just follow the directions.

The correct way to do it is how dc4 said except you should be using kitty hair bondo (water resistant) then glaze it. Do not leave 2k on a repair alone as it is porous and will absorb water. You should seal with epoxy (corroson protection), then 2k, then seal with reduced epoxy, base, clear

 

I was always told the urethane primer doesn't soak up water. Few weeks the repair will be repainted just getting all my dents and dings out before full respray. here is some pics of the repair. Doesnt show the filler step though

 

epoxy wont as its a sealer, but 2k will absorb water.

 

Nice repair, good job on the welding!

 

For the mean time I may just get some vs 4 or 5 sealer to lay over top the primer to keep it from soaking up water til I can get it painted

 

me and my friend are going to cut my rust spot out on my rear to and weld in a new plate