A friend of mine used lizard skin.

I'm probably going to get the underside of mine done with rhino-liner, and while it's in for that get the interior floor done with the same.

As for my shop floor, I sealed the concrete when still green. I'm hesitant to paint it because the first few steps in the door during the winter can be killer slippery as it is.

Have you ever used Chassis Saver. I help my buddy redo his truck box last year. The most important item when applying it is the temperature of the room and the metal be (I think it was 70 Degree F.) The reason is to minimize the probability of any trapped moisture on the metal being painted . We applied it with a brush, when it was finished and cured , you would almost think it was sprayed on, nice job. I am so impressed with it, I have already purchased a gallon for the 1950 project. From what I have learnt it is available in black gloss or flat, and Grey. this is what I have been told, not sure though.
Word of caution with Chassis Saver, don't use a brush right out of the gallon and get any of the product on the rim of the can. The adhesion properties of chassis saver will bond the cover to the can. Take the volume of paint to be used from the can and clean the rim with a cloth.
I have also used Gator Guard, with good results again the temperature thing, messy product.
I think the most important issues are being clean of oils and temperature.

Good luck

Oh by the way , my floors are not painted YET

Regards
Dale