The bigger the base, the better.
I tried a 5 gallon bucket for a 36" Ku dish.
With the dish at chest level, it seemed okay, but heavy wind tipped it over.
Not suitable for use with a motor.
edit: (some used a shallow plastic wash tub with larger diameter)
Lowering the dish to knee level worked better.
So did using a 20" dish for DBS reception.
(actually made up the bucket back when I subscribed)
For a 6' or 8' dish, you probably want to get the center of the dish down around 3' or 4' off the deck.
What's been successful for some, is a regular wooden pallet.
Mount the (short) pole to one corner, with bracing to the two nearby corners.
Then you hang the dish so the corner furthest from the pole points to your TS.
Look at pictures of non penetrating roof mounts (NPRM) for inspiration.
I have recently seen very strong molded plastic pallets.
Whatever you use, you'll want some cement blocks on top for stability.
.