You could just stick with a Rubbermaid grow this time round and build a box for next time and use it with the T-5 fixture..All you'd need would be another 18gallon tub and stack them top to bottom.

If you were going to do this I'd probably leave the reflector out, because it would reduce the overall height your plants can grow by too much.

Others on this forum have modified vanity light fixtures like this Amazon.com: Sea Gull Lighting Center Stage Four-Bulb Vanity, Brushed Stainless Finish #4738-98: Furniture & Decor

and mounted them on the top Rubbermaid container with excellent results.

Also, do those green pots have holes in them? It looks like they don't in the photos, if they don't you'll want to drill holes in the side at the bottom to allow for proper drainage.