Hey I looked all over the body and finally found rust. Under the spare tire i guess water got trapped and theres like a 5cm wide hole and rust around it when i tap on it with a screw driver more falls off it gets sturdy about and inch away from the whole what would i do sand down the rust then spray some primer or WD 40 on it to keep it from rustin further and later bondo it up?

For a cheap fix you could scrape the rust away and DP-40 it or something in that nature or have a sheet metal plate welded in (although i think the gas tank is pretty close so obviously take the necessary precautions). My personal saying is "bondo is bad" but then again it's in a spot where no one would know.
My last supra had a leaky targa before i bought it and i had no clue. it had the same rust spot as well as many others in the floor board itself . I never put a dollar in the thing after that (sold it as a parts car) so i cant tell you from experiance.

I got bored pulled the carpet up and all that don't have rust anywhere just in the area where the spare is i just want it to not rust any further i could personally not car bout even havin a spare i want to just cover the whole were the spare goes and maybe just put a system back there just something small but the dinky board that sits on the spare aint worth a dam i sat in my trunk to get to the speakers and i almost broke it.

I bet you if you check the body above the back tires, the wheel wells....you will find rust. Supras are notorious for it.

Or it's something easy like leaky tail light seals.