I don't think the cleats alone are sufficient for a base unit. The top cleat could easily fail if the counter is stood/sat on, used as a workbench, or sees other typical garage uses.
I would add a 2x4, on edge, between the floor and bottom of the cabinet, about 4" back from the front face. Since you are worried about it getting wet, only attach it with 2 or 3 screws through the bottom shelf so you replace it as necessary. Trim and/or shim the 2x4 to fit snuggly betwenn the floor and bottom of the cabinet.

Ok..at least I got an answer..

My backup plan was to actually use galvanized pipe flanges screwed to the bottom of the cabinets, then a nipple with a cap extending downward to act as an adjustable leg. I wouldn't have to worry about it getting wet..

I like the pipe/floor flange idea much better!

yea, but that's about $10 a leg. So I'm debating on if I can get away with one leg per cabinet. I probably will put them under the sides, so I can reduce how many I need.

I have the exact setup you desire. My garage has a concrete stem wall about 12" off the slab. This makes a nice little 3" ledge at the base of the wall. I made some solid cabinet boxes, 3/4" sides and back, dadoed. 4 drawer tall stacks and a catchall countertop. (intended as a workbench) That sucker is solid, doesn't budge, even though it is simply screwed to the wall and rests 3" ledge at the back.

Properly supported at the back is all you really need. You can build a strong enough cabinet box, all the support can be at the rear. Use 3/4" solid backing. If the thing feels flimsy, add a pipe here or there. You're maybe over designing the thing. It is only garage storage. Save your money on that frenchy thingy. I call those z-channels. There are many kinds to choose from, but you don't need it for a garage!

Thanks Aidan. The "z channels", or French Cleats as they are really called, are very simple and extremely effective for heavy weighted items. You just take a 2x4 and rip it on a table saw w/ the saw set at a 45 degree angle.

The design is such so the weight is forced back and against the wall, and also allows the cabinets to be modular. Meaning it can make it easier for me to detach and move it to a new house or a workshop, if I ever build one.

I was gonna build them very similar to how you're suggesting. 3/4" ply and dadoed. I was also going to begin w/ just the cleats, then like you said, if it feels flimsy, put a leg under it.

I got my idea to float it based on this link at garagejournal.com I was also going to be using pocket holes and glue to put the cabinets together.

I know they're just garage cabinets, but I'm using this as a starting point to learning cabinetry a little better.

If you are site-building the cabinets, I think the french cleat is a wasted effort. You can bolt a continuous 2x6 to the wall studs at cabinet height, then attach the cabinet boxes to it with either metal plates or dadoes and notches with screws. The 2x6 would get a 3/4" notch halfway deep at each partition site, and the partition would get a corresponding 5.5"x3/4" notch to give the joint. Add glue and 3 16d nails and that's stronger and more stable than the cleats; that system is only applicable if you want the cabinets to be easily removable, and install ready-made boxes quickly. The bottom cleat adds little, as the bottom of the cabinets is being naturally pushed into the wall anyway. The top attachment is where the cabinets are being pulled away from the wall, so concentrate your strengthening efforts there. If you're clever you can build these cabinets in with a greatly-reduced amount of sheet goods. 3/4 ply all around is best, because it allows you to use single partitions between segments. Work in a 2x4 for a continuous front edge rail, and you will have the foundation for a strong workbench top.
I would fit the bottom shelf into dadoes in the partitions, since there is no base for support; perhaps even add a 1x2 cleat down below for more strength. A rear 1x4 (instead of the upper 2x6) will give a place to secure the bottom shelf all along that edge, and if you add a faceframe, that will help the front edge. You need to think through the spans and the load for the bottom to avoid sagging.
You can get hinges that allow doors to be mounted to both sides of a single partition, or you could add a continuous faceframe to the unit and hang doors from it.
Casey

Where did you find the floating base cabinets? Looking for some for my kitchen.