Basement floor replacement under fresh water tank

[AikenRacer]

The floor underneath my fresh water tank was rotten. Just demo'd it. Pulled out the water tank. Plan is to clean up the metal support structure, put in a new floor and install the water tank back. The replacement floor will be about 4x8' with a cut out for the dump valves. Couple of concerns..
1) What do I use for the flooring? Need protection from road hazards on bottom and it needs to be strong enough to support a 6' x 4' vinyl water tank (there are 2 metal cross braces). Thinking about a sheet of marine plywood.
2) There was no drain anywhere on the old floor. Should there be one and if so, what kind?
Any comments welcome.
Thanks!

[fuzzyface]

I would use treated (yellawood, wolmanized) plywood, probably 5/8" thick.

[Effy]

I would try and find the source of the previous leak to mitigate the risk of it happening again.