If you worry about rocks and such bashing your rocker panels to the point where you cannot open the doors, then you have probably thought about getting Boulder Bars.
Most Boulder Bars attach to the frame extending out to protect the rocker panels. There are some disadvantages to those types of Boulder Bars. They can cost more than $100, reduce break over angles/ground clearance, and weigh quite a bit. One of the advantages to this type of bar is that they usually protect the rocker panels quite well.
If you have an 85-91Trooper, there is a cheaper alternative. These Boulder Bars are inexpensive, do not reduce ground clearance or break over angles, are quite light, and relatively easy to fabricate and mount. The down side is that they will probably not provide the protection that frame mounted Boulder Bars do, and any impact loads are transferred to the body and not the frame.
This is the prototype. They are welded to the bodywork. It turns out that welding to the body is a bad idea, since replacement will be difficult.
I try not to drag mine across the rocks, but have some pretty stout impacts on them without deforming the Boulder Bars, or the rocker panels. If you drive as if the rocker panels are unprotected, then these bars should prevent most of the damage from an unintentional impact
They are made from 1"x 2" x 0.120" square tubing. I measured from the bottom of the front wheel well opening to the bottom of the rear wheel well opening, along the rocker panel. Then I cut 2 lengths of tubing at that length. I have a power band saw, so it was easy for me to do these cuts. If you don't have access to tools like this, then when you buy the steel, have it cut to the lengths you want. Most steel yards charge about $1 per cut. That is cheap compared with the effort required to cut this tubing with a hacksaw.
Once the tubes are cut to length a bevel is formed at each end.
It's difficult to see in these photos, but I drilled a 1/4" hole through the side of the tubing on each end of each piece. This hole is about 2 3/4" from the end and drilled so that the outer diameter of the hole is adjacent to the inside edge of the tubing. Then cut the tubing along the inside edge of the tubing to the hole, and cut from the end of the other side of the tubing to the hole. This operation results in a "fishmouth" on the end of the tube.
Use a grinder to bevel the edges of the cuts. This bevel will help ensure a good weld.
Then bend the flat side down to close the "fishmouth".
Weld and grind, file, or sand smooth. Repeat this on each end of each bar
The Boulder bar's top side will fit against the rocker panel. The inner edge will fit against the body seam that extends about 3/4" below the bottom of the rocker panel. Instead of welding the Boulder Bars to the bodywork, this time I will use screws and construction adhesive. That way if the bars become damaged, they can be replaced.
In order to screw the Boulder Bars to the body, Pilot holes will have to be drilled into the bars. DJ, for whom I am building these bars, wanted 7 screws to hold the bar to the rocker panel. So starting about 4" from each end I drilled 7 evenly spaced 7/32" holes through the wide sides of the bars.
Then inorder to accommodate the socket used to drive the screws, 9/16" holes have to be drilled in the bottom of the bars. The hole sizes were selected based on the size of screw that DJ intends to use in attaching the bars and the size of the socket needed to drive those screws. Your hole sizes may vary.
Clean,and paint or Powder coat, and they are ready to install.
Place a bead of constructive adhesive along the inside edge and top of the Boulder Bars and press into place. Make sure the ends of the Boulder Bars are where you want them. Then Starting at the center hole, screw the bars to the rocker panel, alternating holes out to the ends. Then using self starting screws screw through the weld seam into the inside edge of the bars. Stand back and admire your work. Please note that the construction adhesive may be overkill as far as attaching the Boulder Bars to the rocker panels, it may make installation easier.