looking for simple plastic quart or gallon sized weatherproof UV proof outdoor bag like ziploc

What are you using it for ? Camping supply stores carry things like that. John T.

It's to protect an antenna matching transformer that I need to have access to occasionally.

Would these "boots" (or similar) work?

Afraid not. My unit is way bigger than those, about 2x3" or so.

Have you looked at stuff sacks in an camping store? They are waterproof and should hold up reasonably well. They usually are drawstring bags.

There might be something in travel accessories too. TSA likes toiletries in clear plastic bags. I use gallon ZipLocks but someone may have come up with a more specialized solution.

I'd probably be looking in the camping/hiking/outdoor stores for a weatherproof container that can have a couple holes drilled for your cables.

These cord boxes seem to come in too-big or too small sizes :

Would it work to make your own out of a pvc pipe nipple and a couple pipe caps? Put it all together then drill whatever holes you need for the cables. Cut the assembly lengthwise to make halves. Use a couple hose clamps to hold things together when you have them in place. Maybe just use a pipe nipple and a single cap.

how about a Hershey's Cocoa container:

Look at one of the gray NEMA 3R junction boxes and use the appropriate cord grips for the cables. They have gasketed covers that are rain tight and listed as U/V protected.

Use the right thing for the job? That ain't no fun.

You will find the sun kills those pretty fast. Even white drywall buckets will crumble after a year or two in the sun here.