Thanks guys! It snapped on like you said it would. Just quite a bit more force than I was willing to apply without knowing what I'm doing.
BTW. The dewshield is metal. Threaded on the inside.
I only got about 5 minutes between the clouds. Caught Jupiter low in the sky (23 degrees); too low to really impress, but looked good at highest magnification I can get, 133x; some false colour probably because of atmospheric aberrations. Then I checked out some bright stars, with unbarlowed 15mm and 9mm Ploessls (40x & 67x). Crisp, sharp, very nice; not like the ugly fuzzballs I see in my GS 8" Dob.
GS Superview 30mm performs well too with this scope except that I need to have the focuser all the way in with the 2" mirror diagonal.
I do need to organise a mount for it now. I was using a camera tripod, which would be fine for birdwatching, but won't be much good for astronomy, unless perhaps I can get the altitude motion well balanced.
Like the silky smooth Crayford focuser. Though, unlike the advertising hype would have you believe, there is significant backlash with the tensioner on; which needs to be on when viewing much above horizon, because otherwise the focuser just slides out under the weight of the diagonal.