It would be cheaper and easier to build a shed for the tank. It will be protected from UV. My experience is that concrete less than 4" thick, whether reinforced with chicken wire or not, is not going to be structurally sound. It'd be like stucko more or less, and won't tolerate encapsulated thermal movement.

If you really want to overcoat your plastic tank, this would be my recommendation:

Polyurea

You can get some excellent UV protection. It has a lot of other beneftits as well, all much better than the concrete and chickenwire approach. I think you'll also find it can be quite competitively priced.

Polyurea is darned near as impervious as it gets. Blast might want to chime in on this, as he's the chem expert, but my experiences with it have all been quite favorable. It is used a lot for ag containment in eastern Washington.