I stacked three leftover 4x4 wood pieces together on each side and then cut the ends at an angle to drive over. These ramps than have a couple pieces of 2x4's running vertical on the inside edge to hold them together, then I ran a couple bolts through the 4x4's and into the side of the fenders. I've been using this setup for years and have never had a problem.
To remove them for hauling a car or something, you simply remove two nuts on each side and pull them off. They are plenty light enough for one person to easily move them around. The other nice thing is that I ran 2x4's cross ways between the two ramps to make a little firewood/parts holder in this area.
The problem with just reinforcing the stock fenders is that they are too far apart and only about 2-3" of the tire on each side would make contact with them, making it really hard to load and unload without having a tire slip off.
Making more permanent inner fender extensions/ramps are a pain if you ever need to hauls something like a car that won't between them.
I originally thought about removable fenders, but decide those would be a pain. Especially since the correct weight distribution of the Blazer on the trailer would require either perfect placement of the rear tires, or pull the front tires past the fenders, get out and reattach the fenders, and then pull rest of the way forward. If the rear tires were slightly off center you coundn't get removeable fenders back on.