Lou, you will get what you pay for. The best tool boxes I have seen are WeatherGuard, but I don't own one because their sizes did not meet my needs. I have a DeeZee in one truck and a Husky in another truck (Home Depot house brand, manufactured by Contico). DeeZee has several quality levels, and their top of the line boxes are pretty good, but their "economy" boxes are pretty cheesy. I also have a custom aluminum drawer unit made up by Ainley Kennels, and it is top notch. The Husky is OK.
A steel box will be tougher than aluminum, but will rust over time, especially with heavy stuff sliding around inside it. Unless I had a way to separate guns from aftermarket jacks, I would not carry my guns in the box. You might want to bolt the jack to the floor of the box with a couple of stainless bolts and wing nuts to keep the jack from sliding around; use anti-seize on the wing nut threads so that you can get the jack out when you need it. With any cross-bed box, I prefer a full width lid: easier to get stuff in and out and fewer ways for water to get in. If you get an aluminum box, you can stiffen it with a sheet of 1/2" CDX cut to fit the floor snugly; add a strap so that you can pull it out and it becomes a traction device when you get stuck in mud. Depending on how the aluminum box mounts to your truck, you can also stiffen it with some strips of 3/16" or 1/4" aluminum plate bolted inside under the top lips. If you get a cross bed box with a full width lid, make sure you have two gas struts, rather than just one in the center. The center strut gets in the way and limits your ability to carry stuff. If you get a cross bed box, a rail mount will allow you to still carry things like plywood and lumber slid under the box. You can increase your ability to slide things under the box by installing the box on pieces of aluminum rectangular tubing mounted between the bed rails and the tool box wings. Rail mounted boxes can be easily stolen by anyone with a wrench. You can minimize that possibility by mounting the box with Yakima accessory locks installed under the rails (same lock used to secure accessories to a roof rack system); I think they are built to fit 5/16" bolts. A bed mount severely limits your ability to carry long items.
Whatever you do, DON'T BUY PLASTIC.