Well, let me say this, no it was not a " difficult " mod but it does >>take a lot of time, if you want a great looking job when you are through. What we did was put a sheet of typing paper inside the smoker on the wall so we had a place to mark on. The rotisserie is centered front to back, for that we used a tape measure . The side racks in the smoker have a " dip " in them, we are right below one of the dips. The measurement from the back to the hole is 7 1/8 inches Then we used a square placed along the side and resting on the bottom to get a stright line going up that we marked on the paper. With the tape measure, measure up from the bottom 19 1/4 inches where the lines cross is where you will drill a SMALL pilot hole >>from the inside out. NOw use a 15/32 drill bit and drill ONLY the outside, then with the same bit, drill the inside. Move the paper to the other side, yu will never get it in the same place so take the measurements over so you get the hole in the >>same place. Again drill a small pilot hole. When you are ready to mount the brackets, another person comes in handy because you need more hands.
I should tell you, the rotisserie we used is a model 60090 made by Grillpro from www.grilpro.com, this is a HEAVY DUTY unit and they are not cheep ! But they are the best rotisserie we have ever used. It comes with mounting brackets you need but not the screws you need. We used short screws so they did not go through to the inside. ( I see the photos are reversed the 2nd one should be first. When you order your rotisserie order a second pair of " prongs " there is enough room in the smoker to do two 4 pound checkins at a time which takes two sets of "prongs " looking at the top photo, this is where you need the extra hands. Put the rod for the rotisserie through the holes and have someone hold a bracket in the right place and the other person drills the hole for the screw and puts the screw in. When you have the first screw in then use a level to be sure the bracket is stright up and down and put in the rest of the screws and do the same on the other side. Now put the end of the rod in the gear motor and turn it on, look at the holes in the side to see where it is rubbing and with a stone in a drill or dreamel tool, ream out the hole, do the outside from the outside and the inside from the inside.