Bracing your enclosure or wall
Yes, steel rods will help you to a degree. I've been using them in boxes as well as walls for years now and gain every time. Even adding M10's to a 2 cube box showed a 0.5dB gain.
The basics are, the weaker the walls being tied together, the greater the effect.
Example: Tie 18mm walls in a 4 cube together with M16 rods and you will gain large (say 0.5dB). Make the same box with 50mm walls and tie them together with M16, and you'll get little effect (maybe 0.1dB if lucky).
As for position, obviously position has something to do with it. You want the rods in a position to strengthen the weakest part of structure. I always use 3 rods, one next to each sub, and one between them. This is because when you cut the sub holes, the baffle looses a lot of structural strength. The rods are there to help.
You may lose some efficiency with rods, but I doubt it. M16 steel rods are bloody strong and only 16mm thick (M = Metric, 16 = Diameter in mm). Using 2"x4" planks inside would hurt for sure, but not the rods. If it bothers you, sleeve them in tight fitting PVC pipes.
I experienced a 1dB gain in my wall from adding 5 2" x 4" planks (externally), a second back wall (covering planks) and 3 M16 rods. I hope this answers your questions.
Oh one last thing. Rods aren’t magic. If you build a weak enclosure out of insufficiently thick materials (Eg. a 6 cube box from 16mm MDF), the rods aren’t going to help much as the structure of the whole box is too weak. The idea of rods is to tie a weak part (Eg, baffle) to a strong part (Eg. back wall) to brace it. Bracing a weak bit to a weak bit won’t help much.