Personally I'd be asking why they only lasted 12 months, 1000 km's is nothing.
The first set I changed out on my GU had done over 220,000 kms and weren't chewed out, they were just getting brittle and they were the original rubber ones.
You'll find the urethane bushes "noisey" due to being more rigid.
The weight of the Chev up front won't bother the trailing arms in the rear very much but the torque of the Chev might with the extra strain put on the twisting of the rear diff.
Likewise the weight of the Chev shouldn't bother the radius arm bushes but then I don't know what caused my 2nd set (see below) to go out like this either because I still have the ZD30. All I could say was misalignment because they were the 2 degree caster correction ones.
http://i1224.photobucket.com/albums/...617_084054.jpg http://i1224.photobucket.com/albums/...617_084144.jpg
Did you install the new trailing arms or did pedders? because from memory, they can be put in the wrong way..
Cheers
Craig