Well, I can share my experience with you at least; you can decide whether it's worth anything. I'm just a diy'er and did have a pretty fair success with my situation, which was very similat to yours in that the panels were beginning to rot in the bottom section, AND they were a pressed-board type of thing.
First thing I did was to cut out a section of one of the panels to see what it was, and to investigate whether the actual wood frame under it had also rotted: It had not rotted.
It was 1/4" (15/64") in its unrotted, paint-scraped off section, so after a bit of thought, here's what I did:
-- Talked to my local lumber yard: They knew what the material was, had it in stock, but could not order panels for me specifically for that door.
-- Checked with the local Overhead Door Inc. place and they verified what the lumber yard told me, and offered to get me panels - a some god-awful price!
-- Bought the stuff from the lumber yard; being the same material, it painted up well and now looks great, like nothing was ever wrong.
-- Lumber yard told me there would be wood "pieces" inside surface of the door, same as the windows, and just pull them off, cut & replace the panel, and done! Only, well, there weren't any wooden hold-ins: It was solid wood, apparently having the panels installed during assembly. Not really surprised, but I was disappointed.
-- Grabbed my router, and routed out the inside section of the part holding the panel in. Inside surface, of course. Now they slipped out rather easily.
I did this one panel at a time, BTW, with the door still in place, and still held by the normal suspension springs. Didn't want to take the door down if I didn't have to! I didn't have to.
-- Put in the new panel, cut to exactly the size of the old ones. Old ones by the way were glued & tacked; I thought they'd be loose like cabinet door panels, but they weren't. So, I glued & tacked the new ones in (after cleaniing up the area where they fit of course), then used some old oak molding to make up for the routed-out wood; looks very close to the original.
-- Primed, painted, and held my breath. That was about 5 years ago, and it's still holding well. I replace all 6 panels in the bottom of the door (a 9 ft door). I see the other door, same kind, starting to show signs that the material in the panels is starting to swell, so assume it's time to think about doing that one too, now. Thankfully, no panels except the bottom ones have ever showed any signs of problems. Well, except the one I backed my boat into and the prop sort of pushed one in a little. That's on the other door I haven'\\t worked on yet .
SIDENOTE: While I had the door opened and stably positioned like that, I took a few minutes to check the joints where the bottom of the frame met the side pieces. It wasn't as rock solid as the top corners were at that point, so I also slipped a piece of pt wood over the joint and, being careful that it could never interfere with the lift wires, fastened it with glue & screws. That bottom rail gets a little extra pressure applied because the wires connect to a bracket right at that point.
Ask me in another 5 years or so and I'll tell you whether I did a decent job or not .
Be EXTREMELY careful, if you work on the door in place, to firmly and fully block it so it cannot open or close on you as you work on it. That's why I left the springs etc. all connected. I was afraid that extra pressure would cause me a problem, but it didn't seem to. No cracks in any of the paint, no movement of any parts visible.
YMMV of course, so please keep in mind this is my experience, and only mine. I've had people say I did a good job, but ... them's sometimes famous last words, I guess. I used vice grips on the tracks to hold the door from going up, and tacked boards to each side, under the door, to hold it open at a convenient height to work with. The farther up you let the door go, the less weight there is on the overall frame. Oh, I forgot: The door opener I reattached too, and let it help hold the door, then I put the grips and boards on to add extra hold.
HTH,
Pop