I'm in a similar situation, but replace horses with UTV's & snowmobiles. As a stop gap till I find the perfect truck camper. I've used the Kodiak truck tent last summer and will probably use it again this coming summer. It is a bit tedious to setup but once up with a inflatable mattress it does the trick. Weathered a few severe thunder storms in it and stayed dry.
My ideal setup would be the Capri cowboy or Rayzr FB/FK. But they still push the weight limits. I'll have to investegate some of the other options you've found. And see if they could work for me.
