Sorry i'm not answering your question directly. While I still think it might be good to experiment with one of these carts.
I've thought about using something like this, but I think it's easier to get a good external metal frame backpack and tie the tree onto your pack. Most of the collecting i've done has been up in the sierras and dragging a cart up and down the mountains would be more difficult. Really rocky areas might be too challenging with a cart and if the mountain/hill is too verticle it could be harder too. Either way your going to get a good work out! I think the more I collect, the more I learn to keep things simple.
This is just my opinion i've seen some good collectors in Europe using these carts. But I also know some other good collectors tie trees onto their pack. Good luck on your trip!!!