the "aluminum bondo" you are talking about is the final cry to patch up a rust bucket that has past a point of no return....
It does not block in well, fillers dont adhere well, epoxys, urethanes, etch primers dont react well long term....
Do yourself a favor and keep it simple.. get a nice solid metal foundation on your car and go from there..
Fiberglass/resins, aluma bondos,fiber bondos etc. will in no way fix your car or make it look good.
My filler of choice is U-pol gold with U-pol gold glaze.... its a production filler but wont shrink or leave feather edges and pinholes...