So if I got this right, you want to slap 4 50x75 bases together to form an arachnarok spider. But instead of using 4 bases use one base the 100 x 150 base. I think you would be better doing a diorama using 4 bases together and as the fight goes on you can move them about. The main problem stems from using wrong base size and having a fixed model instead of a unit. You can mess around with it some, but I really dont think it will work as you present it. But eh, I have seen more bizarre ideas come to life, hell I have made a **** ton myself.