It seems that most Blazers I've bought have broken door panels. I've had to repair a few and this is how I've done it.
I bought the smallest fiberglass repair kit at the auto parts store. Once the door panel is out, I stand it up to align the crack. I spray some brake cleaner along the crack lightly then let it dry,to clean the surface. I then take some pvc cement and dab it along the crack and let it set up overnight. This allows me to handle the panel the next day with care to the laying position. I have an old sleeping bag to lay the panel on and a shallow box to support the upper portion. Cut the fiberglass to size and lay on the panel then mix and apply the resin. I do the longer cracks first then add two layers of fiberglass in small squares to the areas where the bolts will go through the panel to support the arm rest. I'm guessing these bolts were not removed and the panel was just yanked off the door, thus breaking the panel. When re-installing the panel I use a larger thin plastic washer before the screw. I re-sized these photos but if I need to go smaller, I apologize.
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Good post. Good ideas.

Use ABS plumbing cement instead. It will hold much better under the fibreglas as the panel is made of ABS
Here's how to test a glue/epoxy etc.

Clean a small hidden surface. Put a thin layer of the substance on and let it set up. After it has dried/cured then pick it off if you can.
Strong holding, it doesnt want to come off at all.
Medium, it will come off but you can see where it was by roughness/dullness of surface it was on
low- none, the surface it came off is still shiny or hard to tell where stuff was.

I use plumber purple primer on about every plastic related fix. Found out it even works with mirror attach along with regular gel superglue.

 

actually i was about to see if anyone had a door panel, and like you said most are broken, and mine actually completely split today, but thanks for the info, could you send me some of the higher resolution pics to my email? This is something that i have to do unfortunately

 

It will be harder on you to keep the two halves together. In my pictures you can see the light shade of white above and below where I repaired the panel. The previous owner used duct tape to assist in keeping the panel together. I used some goo off to remove this glue. In your case I would clean the panel and use some duct tape in areas to hold the two halves together while repairing other areas along the break. Once the entire break has been seamed, I would add some material perpendicular in a few places to give extra support.

 

Just finished repairing my door panel following these instructions and it turned out great! Thanks a lot.

I went to the junk yard hoping to find a replacement and every door panel was already seriously cracked like mine. So this was a life saver.

 

Great Job! What I found is that the Dorman/Help plastic retainers just simply DO NOT work to hold the inner panel in place! So I bent over and took it hard for the dealer fasteners($1.83 ea for a .15 part) and they did it! But they worked! Headache over for $12!

 

Have to agree about the Dorman retainers. The plastic is too stiff and breaks too easily. I will have to buy some of the originals myself!