My rear big bumper had damage after a knock and run

So I took it off and was about to order a new one, but I found the bumper had acted like a water trap and the bodywork didn't look great behind it.
I've got the fully body kit on my van and it was an after market addition (by the previous owner).
I'm concernd the kit is acting as a rust accelerator and I'm tempted to fully remove it and replace with standard bumpers
