It is not a bad idea, although exercising with you own weight, doing pushups, situps, and that kind of stuff, is gonna help you way more. Think about it: lets say that you weight 180 pounds; when are you gonna actually grab a weight at the GYM that actually weights 180 pounds? Well, everytime you do a pushup, you are lifting all this weight. Plus, being inside the GYM can be VERY boring. the idea that you'll be sorrounded by hot girls, and that you'll become a rock, and all of that, is false most of the time. The girls are doing their own thing, and you can become even stronger outside of the GYM. You can do 10 sets of 30 pushups every two days, and you'll be a rock in a few months (I did it when I was twelve, plus 2 hours of swimming, I became a rock). It may sound tough at the beggining, but think of the other 14 players that your arms are going to protect when you hit a ruck! And you can do this for all the parts of the body, just make sure you find the right training, and that you put your heart in it.
Do alot of circuit training to keep your speed and mobility as well as build strength. But being second row you want alot of power and strength, develop raw all over power as well as core strength. I'd suggest dead lifts, squats etc. exercises of that type!
