I've done more than make a cart from a wheelbarrow...or maybe you'd call it less. My partner and I used a wheelbarrow to pack an elk 4 miles on a logging road and it worked great. Granted, it was 90% downhill. Going uphill would have been an entirely different beast. For the short uphill sections of the road, we tied a rope on the front for the other guy to pull.
Someone said you need 2 wheels. That's fine if you're on the flat on a road or wide trail. In the mountains it'll get you in trouble. You'll be too wide for many trails. You can't get between rocks and sidehills will roll you. The only way you can use 2 wheels in the mountains is to have them in single file and that creates problems of it's own.
Don't use a Walmart wheelbarrow. Get a good one. It'll be strained a lot more than when you use it at home and the cheap ones can't take it. I can tell where you can find a pile of old wheelbarrow parts about 2 miles from a trailhead.
