tizwozliz I'm no good at this put-things-out-during-the-day-bring-them-in-at night business. I move things from propagator to porch window, to "warm" end of unheated greenhouse to "cold" end of unheated greenhouse. So what I've done at the moment is to plant out everything from the cold end of the greenhouse secure in the knowledge that they've got a few warm days to get used to the outside.
Germinated - broad beans (about 6 inches high, soon to be planted out)
Sugar snap peas
Courgettes
Tomatoes
Chilli
Lettuce
Radishes (sown in containers outside)
I'm making more use of a propagator, which really does speed up germination at this time of year. But gives you a whole extra step in the acclimatisation thing.
Rhubarb could you put out a request on your local facebook page for old pallets? If you could get someone willing to deliver, and mark out with chalk somewhere convenient to leave them, you could then leave them there in quarantine for 3 days before touching. If you're like us, local recycling sites are closed, so there's bound to be someone who doesn't feel like storing surplus wood for the next 3 months or however long it will be.
Try growing the squashes vertically instead of letting then ramble. Or grow in a big container so at a pinch you could transfer to the allotment in July or August (though with shielding continuing to end June, I suspect going out in July/August is going to still feel very dodgy).