Just an update...

I found a local guy who was selling a Sears X-Cargo X-treme which looked like it was in pretty good shape for $99. That seemed like an OK deal considering they are $300 new.

Well now that I have it, I learned a few things. The first is that while it is a pretty decent unit, it does have a major weakness which is the plastic material that the bottom is made out of. The material is too flimsy and after I bought it I discovered stress cracks in the plastic where the mounting holes are. What I did was reinforce the 4 mounting areas by laminating on a few layers of fiberglass mat and resin. I put on a total of 5 layers, 3 on the inside and 2 on the outside, so it's really strong now. I am still getting used to this fiberglass stuff, it's surprisingly strong once it's cured and you can't even see it against the black plastic (assuming you don't leave air pockets or anything).

So anyway, mine works well now, but I wouldn't really recommend this unit to anyone else unless you are willing to reinforce the mounting area like I did. I guess there is a reason why it is cheaper than most fancy carriers.