Protecting Seedlings
 

I have no need for protection from the cold. I am in Miami, Florida. The growing season here is winter, so I need to start seed in the last part of summer, with temp in the 90's and a lot of rain. Most of my starts were destroyed. I have to start seed outside, so I need some sort of shelter for the starts and small seedlings. I need ideas.

I use the 32 oz Gatorade bottles with the bottom cut out to protect my seedlings. The only downside for you is that it also acts as a greenhouse.

That might work with single seedlings, but my main problem is with flats of freshly sprouted seeds.

The standard solution is a lath house. Or use some old bamboo shades to block the sun. If you don't have space for a structure, do you have a shady spot? I'd imagine your seedlings would get enough light even in the shade. Under the eaves? North side of house?

I don't have heat problems, but I use old window screens over translucent plastic bins to protect seedlings from birds and sun and to cut down on the slug/snail damage.
With heat, if you had a framework (I use kitty-litter bins, which are easy to come by), you could place screens on top and, if needed, drape some screening material over any sides that get any sun. Or use an umbrella. Or put them under a patio table, esp. if it's translucent.

For rain, I bought a piece of plexiglas. Or you could use the covers from translucent plastic bins. I start my tomato seeds during the (cool) rainy season, so I sprinkle cinnamon powder on my flats as an antifungal. Another cheap antifungal is chamomile tea. In your climate, you also want to maximize air flow. Do you have a spot that can catch breezes?