I can't really tell what your unit is - is that a zip-up
type plastic greenhouse next to a water heater?
If that is the case it should work just fine. How
will you mount your lights?
its a zip up front, i just but it beside the heater to take a picture lol theres a poll across the top in the centre thats where i will hang the light with chains for adjusment
Keep in mind that T8 flouros provide effective light coverage pretty much only in the 'footprint' directly below the fixture. So with one fixture, you are going to be limited by the shape (usually about 6-inches wide). It would be way betta to mount a second fixture side-by-side so you have 12-inches width. Then you could fit two trays under the lights lengthwise.
The mylar or foil will help hold in heat and also distribute the light, which does widen the 'footprint' a little bit.
Another consideration is the height of your enclosure. Your T8 lights will be most effective about 1 to 2-inches above the tops of the plants. So you're going to have to dangle them about 4+ feet or better yet, put in a shelf in there to bring grow trays closer. With a shelf system, you could eventually add a second deck also, with another set of lights under the shelf.