I still haven't tested the Sandtrakz with the rigged TI on soft sand, but thinking the TI's weight would be better handled with 4 wheels (especially after watching Nohuhu's above video) I recently purchased a second C-Tug with both sand and hard wheels. I wanted to try Nohuhu's suggestion of joining the two carts to make a 4 wheeled cart. I also wanted it to double as a trolley cart for transporting all our camping gear to the waters edge.
Much like this Wheeleez cart

Joining the carts was easy. After a trip to our local hardware superstore I came home with 2 x25mm water tank flanges and a 25mm x300 poly riser pipe to suit,

For strength I added some 25mm bimini tube which fits OK inside the riser tube after some persuasion with a mallet. Adding a bevel with a file to the tube end helps.

The two carts are now easily joined together and can be separated in seconds by undoing the large flange nuts.


To get the tray I also purchased a cheap wheelbarrow.
Adding a bungee button each end of the tray makes for simple attaching with bungee loops



The tray is big enough to carry large objects

or they can be strapped direct to the trolley

Unfortunately fitting the four wheeled cart to the TI proved not as easy as fitting two singles, so that didn't work out, but I now have an all surface trolley cart for gear carrying that breaks down simply to two separate carts.