I am from a desert climate zone too. Frost covers have worked very well for last several years. Even the occasional deep freezes have so far not been a problem for the covered plants. A few tropicals in containers have also survived well when kept covered in the patio. A jasmine plant in container kept blooming under the frost cover in the patio even in winter.
I have written more details and some other winter protection ideas in this article:

http://www.elpasotwigs.com/garden/winter-protection.html

Here is a link that might be useful: El Paso Twigs

How are things going?

If what you planted is reliably hardy, no protection should be needed, especially if put in ground in spring. Where the ground does not freeze, heaving is not a problem. Attempting to keep plants that should go dormant in vigorous growth mode at the wrong time of year could be extra stress, not helpful. Unlikely in Z8 but worth mentioning. Couldn't tell if you are talking about plants in pots or in the ground? What plants?

If you are zone-pushing Z9+ plants, I don't think I would use any kind of plastic. A pile of leaves is my usual method. Some paving bricks adjacent to the roots (on S side,) or dark-colored jugs of water, dark rocks, can also help keep the ground slightly warmer. Regardless of method, excellent drainage is usually a key factor in successful zone pushing. Wet + cold = rot. Dry + cold = exponentially higher chances of survival.

These are in the ground. I don't think my angel trumpets made it. Even though I had then covered during the times for frost, they still were damaged. They are planted on the slope in my backyard, so water does not stand. I have been keeping my eye on them, & it seems everytime I look at them, they appear to be in worse condition (I still keep them covered). I have my fingers crossed & hope that the roots are in good health. I know they go dormant during the winter, but the trunk & branches are not looking good.

If you mean Brugmansia, the above-ground parts die back, then regrow from the roots.

The trunks are severly damaged. There is mold in a few places, & the branches have turned soft & mushy.

That sounds normal for Brugmansia.

I practice survival of the fittest. What makes it, makes it. I try to plant things that at least do reliably well given the extreme temps that the desert throws at us. I also grow a lot of things from seeds which seems to give plants a better edge in the long run.

The way Louisiana acts, it's practically a desert. Yesterday the high was 25, but by the end of the week comes, the highs will be in the mid 60s 0_o While it is still chilly I need to get out there & prep my garden area for this year's vegetables.