questions for guys who have reinforced their tailgates internally

This write up was done on toyotanation, but it's long been dead, and I'm not a member there anyway so I figured I'd just bring it over here.

Most of the searching I did came up with posts from guys bracing their tailgates with sheets of steel or diamond plate aluminum, which I'd like to do eventually because I hate that noise my tailgate makes when I step on the plastic, but for now I just wanted to do something to keep it from bending when I put motorcycles in the back.

http://www.toyotanation.com/forum/showthread.php?t=170754

He used 3/4 angle iron and some self tapping screws. I was gonna just do the same as he did, but I had a couple questions about possibly making it stronger.

First, are the self tapping screws the best option? I wasn't sure if it would be best to use similar screws, low profile bolts and nuts(so the top plastic guard wouldn't be raised), or just aluminum rivets.

Second, people popped up later and said that a square tube(steel) would be stronger. He went with the 3/4 angle iron instead of 1" because it was the widest that would go and still be able to fit inside without cutting and rewelding the tailgate. Did anyone use a square tube, and if so how thick was it? I feel like the tube would have to be so thin that by the time I got it in there it'd be too thin to really help.

Any experience or advice would be great! Otherwise I'll just grab what I see at the hardware store and go for it.