@relapsed_mandalorian thanks! New garage doors (for mine, sorry) have been on my list for a few years now, so don’t hold your breath.
@kayak23 ta, and thanks for the finish advice. Rustins water-based varnish from Toolstation worked well, though coverage wasn’t great. One heavily thinned coat and one neat coat on the more important bits, and I still had to buy a second litre tin.
I was trying to keep the whole thing as quick as possible, hence using spruce ply instead of MDF to cut down finishing time (dunno whether that worked) and also because I don’t really like MDF, 18mm all over to eliminate the need for framing, and invested in a pocket hole jig. The base is slotted into the sides too. Still took me about a day and a half of work to put together, plus (not insignificant) finishing time.