Is the wall freestanding? How exposed is it? Do you know how well the two skins are bonded? What supports do the patterned concrete blocks have? Some of these walling systems had precast pillars that would be dropped over rebar and filled with mortar or concrete.
In my landscaping days I'd...
Thick timber screwed to stout uprights will be better than glue and laminating. Leave your timber outdoors a while before building so it is acclimated, can get horrible results if it's too dry
Any local community woodlands? Wildlife trusts might be worth asking, they'll be looking to do woodland work before long.
Avoid trees grown on their own in the open if possible, the grain is often difficult
You'd be amazed the number of fixings found in tree trunks that are completely grown over. Most sawmills won't touch garden or hedgerow trees for that reason. I've blunted a few saw chains myself taking out old conifers in gardens, usually where someone put up a birdbox
I'd make a frame like a door liner with the head wide enough to span the gap. Drive some angle iron into the ground either side to fix the legs to, use webbing straps to fix the head in place and hang your gate of choice. It won't win any prizes for fine woodworking but should do the job
I'd be interested to know how it works out. Guessing you've got the cabinet type with a fan pulling moist air out?
This might be helpful
https://arbtalk.co.uk/forums/topic/109727-sauno-wood-kiln-%E2%80%93-any-good/
Never tried that but if you have one big enough I don't see why it wouldn't work. The microwave method is very effective and probably easier on the wallet with the cost of electricity
IHT raised £7.1 billion in the last tax year, or less than 1% of tax receipts. Income tax raised £268 billion by comparison, or around 25% of tax receipts. Ditching IHT would seem a 'relatively' cheap vote winner
Could you drill the door out carefully and add a couple of watch strap pins, pull out the nails and use the pins instead? Makes the door removable if needed too