One step ahead of ya here.
I have picked up some 3/8 thickness, 4 inch wide aluminum bar, that I will cut into 6 inch lengths, and thread a half inch whole in the center. These will be the bases, and will be placed in certain places around the boat. Then, for single holders, I will make something similar to these -
https://brotherhood-of-catfishermen.com/catfish/messages/43781/26308.html?1109569775
with a 1/2 inch bolt to thread into the whole (these will be used for stripers too - hence the large bolt). For my spider rigs, I will either get some 1/2 inch threaded rod, or just cut my own threads into some regular half inch rod, and at the top, have a piece of 1 x 1 square aluminum, probably about 30 inches long. Then, there will be more rod holders made of PVC (probably 3 inch, and they will have 3/8 or 5/16 bolts) on the top, at varying angles. On the other board, you can see my post, and look at the layout I was thinking of. I will post pictures on here when I get finished.
The only thing that my idea lacks that that one has is the ability to move out and in. Mine can tilt up and down, as well as turn both the whole rig, and single rods all the way around. Most of the spider rig pictures that I see on crappie.com didn't have that option, and from what I read, most people thought that if you got the original placement correct, there wasn't much need to have them adjustable.