In looking at my own photo, my earlier description was a bit inaccurate, as I actually used three angles along each side, for a total of six along the sides, rather than four. I used two along each end, so that there was one on each of the four end panels.
Note that while I used aluminum angles, you could also use wood blocks, as the important things are only that (a) the inside distance between the outside edges of the angles/blocks be the same as the distances between the sides/ends; (b) with respect to the ends, it's best if the ends/blocks are relatively close to the middle of the top to insure that the hinges are fully opened when the top is in place; and (c) the dimensions of the sides/ends should be such that the tops of the sides/ends will not interfere with the holes in the top. Note that the angles/blocks can be placed between the holes, as shown, so that they don't interfere with any clamps, etc. inserted into the holes once the top is in place.
As you can see, this approach, unlike the ones shown by Coach.carpenter and/or fyme, is very simple, requires no special cuts in either the sides/ends and/or top, and can be readily adapted to existing tops, like the router table that I have had for several years. Consequently, if you are going to a job site, or you need space in a small shop, you need only have one set of sides/ends and one bottom panel, while you can have a number of different, interchangeable, tops, i.e., MFT, sacrificial top for breaking down sheet goods, router table, Bessey clamp table, Kreg-type clamp table (with T-track), downdraft sanding, etc., basically an endless variety of tops with only a single base. Alternatively, you can have multiple bases that can be stored (folded up) in very little shop/vehicle space. I should also add that if you have an idea for a new type of bench you can easily prototype it by making only the top which can then be placed in position on the base. By way of example, I have built a number of rocking horses for my grandchildren, and I keep thinking that it would be great to have a "sky hook" to hold the body up, while trying to arrange the legs and rockers in position for assembly.
If the photos and explanations were not adequate, I am willing to prepare plans, which I will make available for a nominal price. Also, I have a Shaper Origin, so I am thinking of creating a set of CNC files for it to make either entire units or router templates.
Sandy