Installing some 4000lbs/12000lbs D rings on my homemade trailer project.

This is my $400 homemade trailer I picked up off of my favorite place, FB marketplace. This used to be an old 70's camper that someone started converting into a toy/equipment hauler but never got around to finishing it. So far I finished up the wiring on it and today we will be installing some 4000/12000lbs D rings so we can tie stuff down.
Here are the D-rings I am using: www.amazon.com...