The drainage holes are called scuppers.
Of course the cart is called a scupper cart.
I would be careful with this.
#1 scuppers are a very weak point on most boats. If you put stress on or in them you very well may crack them
#2 How do you get your wheels back into the holes with a loaded yak. Trust me it is almost impossible.
Also be careful the way you trasnport and store it. ALWAYS upside down or on its side, unless you have a cradle from Thule. If not your boat will warp in about 5 minutes. Also dont winch that thing down too tight on the rack, that will warp it too.
Make sure you do not skimp on the pfd and make sure you have a compass or gps. You never need either, till you NEED them
OK thats enough of the lecture Go have fun.