Must be a switch that’s packed up. Somewhere around the bonnet edge, probably a push switch. If you can find it it should be simple to join the wires and fool it into thinking the bonnet is shut.
I have 4x4 pressure treated under my shed but to keep the height down you could use 2x2 or 3x3. Lets air circulate, keeps the floor off the damp and if the bearers rot they can be replaced relatively easily.
I have used these people before for a TR6 windscreen. He fitted it free of charge so he could show his guys how to fit an old school screen. I supplied the rubber and trim. May be worth a call.
https://www.1stcallwindscreensltd.co.uk/
Discs I fitted recently came with a silvery coating and instructions not to remove it. Just a wipe over after fitting with brake cleaner to remove any greasy finger prints.
Mine is mounted in the ceiling but comes on with the light and then runs on a timer depending how long the fan has been on. It does have a humidity setting but we found it to be a pain in the arris. Made by Greenwood.