Tell us how you are doing vertical panels now, and at what speed/s..
Are you bending down to do them, kneeling down, sitting on a creeper, chair,rolling device, or sitting on the ground, and what size pads ??
What grip/s are you using - the horseshoe one or the side screw-on grip??
I am an old school buffer, and learned with the side grip for my left hand and the right hand at the bottom handle of the buffer, and still feel comfortable with this grip, and not really cared for the horseshoe grip over the top.
I have also found that I like my left hand on the side grip as close to the machine as possible and the dang grip that comes with it has this huge circular plastic molded piece that prevents my hand from getting as close to the machine as I would like. But I made adjustments and am ok with it now.
I have found that vertical panels, doors, fenders, quarter panels, etc., are best done starting with a few horizontal passes, to help spread the material, and get it warmed up, and keep doing horizontal passes, until I am about more than halfway through, and then finish up with vertical passes.
You have to adjust your stance, and the way you hold your buffer, to do vertical passes, so how about practicing these types of passes with the machine, off, with a pad, with nothing on it? Just think about how you would do that particular panel, take yourself with the machine through it, and when you have the plan in your mind, then get your material on, and start.
Notice which way you tilt the machine at the end of a pass, and imagine the machine running and thinking is the rotation going to take me the opposite direction or want to keep going when I tilt it?
Just remember that when you tilt the machine the outer edge of the pad is now spinning faster then the middle and this translates to more work/correction/heat, etc., going on for that brief moment.
The Makita starts slow and then comes up to your preset speed so that is nice, and always remember, you can pull away or stop if it wants to drive you in a direction you dont feel natural with. Its all about how much you tilt it which direction, which determines for alot of this, how it will react.
It does take awhile to get all the infinitely possible ways to use this tool on any panel, just take your time, do dry passes without power to get the feel of the machine against your arms and shoulders and back, and you should be fine. Try to keep all your movements smooth, and develop a rythmn from one end to the other, and take it nice and slow until you get that down.
Dont fight the rotation of the buffer, rather, control it by pulling the buffer the direction you want with just enought smooth pressure to keep the pass smooth and straight, so that your media is working all the way across or up and down.
You will also find that if you use this rotary or even the random orbitals alot, you will start to develop bigger, stronger, forearms and biceps, and your hands will develop a much stronger grip. All of this will help you work that big hanging piece of metal and plastic ! Look a the GUNS that Luster and Street Dreams have, - these guys are buff !!
Keep at it, you can do this, and good luck with your project !!
Dan F