I have a JD 2305 also, I mounted a cheap military ammo box ( eBay ). On the front where the bracket allows for weight to be added, With the loader off, have to be careful not to crush it.
Now a warning : I mounted a tool box on my Dads tractor. Right behind the seat. He put a chain in and didn't get it latched down correctly. ( months later ). He was mowing with a rear finish mower and the chain fell into the PTO - this caused a 4 ' spinning log chain, Tore up the fenders, tranny, PTO shaft and mower gear box. Darn near killed him- knocked off his hat !! Reason I mention- when I see pics of a rear mounted tool box, I cringe for others safety-- things go bad quick. Hope this helps.