A poly tarp (one of those blue or silver ones you can buy everywhere) and a roll of Gorilla black duct tape can substitute for a custom sewn canvas cover.
Pull the cable support tube out of its mounting holes in the gantry. Lay it on the water table slats and you’ve got a mostly flat top (or at least you don’t have to account for a two foot pole sticking up 
).
Drape the tarp (a 6x6 or 6x8 will do) over the table. Get it centered. It should not reach the floor & get in the way of rolling it around.
Go to each corner & fold it back against the side in a triangle shape. Tape the hypotenuse of the triangle to the side. Tape the base of the triangle along the bottom and fold the tape up to catch all of the layers of tarp. Repeat for the other corners.
Total cost about $15. Or you can look for a grill/smoker cover that has the right dimensions to cover the top and drape over the sides. They can get pretty expensive though.
The key is getting the cable support tube down & out of the way.
When it’s time to use the table just pull it off, poo the tube back in the gantry and you’re good to go.
Before shutting it down, move the gantry to the center of the table so the highest part is always in the middle of your tarp drape.