Well what a day - bit the bullet and got stuck into it.
I take to woodwork like a lead weight floating on water - its not a natural LOL.
OK screwed and glued two sheets of 25mm structural ply together, did that last night as it was dry this morning.
first thing i did was mark it all out and position the pier for a look.
then realising the jigsaw blade was a bit challenged for the thickness of the ply i went to bunnings - got some more hardware and longer blades and some white spray paint for another project - repainting the black stella seat white so you can see it in the dark.
back to this - it was damn hard to keep a straight cut

but i did my best. after cutting the shape out then fitted the pier for a look and was in awe..... simple amazes me that i was able to do this woodwork - i am woodwork challenged
Al came over late in the arvo and gave me a hand fitting the feet and "product testing with the mount and setting it up roughly. Al will be making me up some resin feet with 6 200mm bolts i bought that also fit the furniture feet i installed - for setting up on really uneven ground.
anyway I will do a little more tweaking and install two more feet to the left and right of the pier in the middle - so that it will be a fully supported platform whether i need it or not