I rushed a small frame build to see if I could get up and running in time to build some parts on a deadline (ambitious kids Halloween costume) and found a decent way to use furniture flange inserts as bolt anchors. The parts are very cheap, $6 for 12 and take almost no work to install.
I have them inverted to offer more support above the surface. The bolts are just what I had laying around and are too long but do the job.
They are screwed down with three 2" construction screws through 3/4" plywood into a 2x4 on its side. It feels very solid.
Maybe this helps someone else.