Our Northern has that system of raising the hoops after you've put the cover on, to tension it, but we couldn't work out how to do it
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Ours (7 x 14 x 4m high) has base rails for attaching the cover, crop bars, bracers at the corners and from the ridge pole to the crop bars, and is the biggest diameter tubing they do (it's a bit windy round here). Check your nuts and bolts after any big wind for tightness. The hoops are held in the ground by poles fixed into concrete dollies - obviously you have to get your positioning absolutely perfect or your tunnel will be on the skew, then will never be properly tensioned - make sure you're good at geometry and your ground is flat. The hoops are then fitted into the ground tubes with ring and bolt fittings.
Pay special attention to ventilation, as even in exposed sites the wind doesn't always blow, and the temp will rocket inside. We have large double width louvres, one above another at both ends, and double doors at one end and a single door at the other, tunnel placed east-west. The lower louvres are a waste of time as weeds and built-up soil stop them from opening easily, plus you can only grow very low crops under them.
Our first cover blew off in a monster gale, because we hadn't attached the polythene quite right. With it all now done correctly it has survived storms just as huge.
Don't scrimp on the cover - get the thickest one, anything else is false economy. Also use the anti-hot-spot tape on all metal/polythene contact, and buy a wide roll of repair tape - it's great stuff, whereas gaffer tape just doesn't work. We had had all sorts of holes punched in our cover, from a sheep's horns, helpful friend pulling long canes out and going straight through, to the cover bumping into the apex of the greenhouse in a big wind (the frame flexes) but the repair tape holds it together as strongly as before the hole.