Taig sells a tooling plate you can screw things down to: https://taigtools.com/product/4-x-14-x-5-8-tooling/ You can also use 10-32 all-thread studs and square nuts in the slots to hold things down; another alternative is strategic grinding on carriage bolts. Strap clamps and step blocks are easy to make on the mill; steel or hardened aluminum both work. Those cam clamps are an interesting alternative; what size are the screws that hold them down, and did you find T-nuts that work with them?