When I saw your small raised beds clustered together (nice approach, and nice-looking raised beds!), I was reminded of a book I read by some Mainiacs (people living in Maine, not unusually-psyched). They grew outdoors all winter. In Maine.
Their secret was "layering", with floating row covers, plus low hoop tunnels, all inside a high hoop house. They figured that each layer gained them something like 5-10 degrees F at the cold point of the night. They hit a wall when they plants were OK on heat, but never saw enough photons to do any growing! They went into a holding pattern.
Anyway, seeing your raised beds made me think of each one with some floating row cover, or else the smallest, lowest PVC hoops that would work: perhaps with their PVC feet INside the bed instead of OUTside as would usually make more sense (get the soil warm during the day and it will heat the air inside all night).
Call either of those "Layer One".
But then put one BIG hoop house over all four beds! Now you could walk into it, close the door, and then uncover the small beds one at a time as needed. And according to the fresh-lettuce-for-market-all-winter Mainiacs, you could get up to twice the warmth.
P.S. If you put your approximate location and other info into "Your Public Profile", they will appear on every post you make (upper right-hand corner). I think it's cool that each time you update those fields in your profile, every post you've ever made is updated with the new info!
"Your Public Profile" is reached through the "head-and-shoulders" icon at the top of the far-left blue menu bar.
There's a more complicated process for putting info into your signature block, below each post.
