OP, basically, you'll get 10 to 1 responses saying everything from "not ideal" to "OMG, what are you thinking"
Would I rather have a big ole diesel to chug along like nothing was behind me? I do (for personal use) and I like it. I also tow about anything a 1/2 ton will move down the road without bottoming out the rear suspension up n over mountains.
I think nothing of hooking 10klbs to an average half ton. It's a truck, it does work and my company doesn't buy me a big ole diesel.
Rock what you got. No point in trying to upgrade trucks right now. Wait a cpl years for that.
The one thing not mentioned yet is the condition of the truck. I'd want it to be in great shape mechanically, not 150k miles and dunno when the trans was serviced last.....
Alos, the biggest factor in how it tows is the size of the box, speed and wind resistance, not the weight (within reason). You could get a 26' "ultra light" trailer that is 5500lbs instead of 7klbs like the one you're considering and it will tow about the same.
