My only advice is, like beesuits, but the best you can afford. Quality differs hugely
This is very true. Cheap is undoubtedly going to be useless. You can save a small amount of money by going for a cover that is buried in a trench at each side of the tunnel, but it is more effort to do (I use a trench). Personally I'd not bother with the "anti-drip" coverings either. I've had both and it doesn't seem to make that much of a difference in my 30'x14' tunnel. Do use the hotspot tape though.
Some tunnels have fixings for the sides of the tunnel (instead of using a trench) that are wood and some metal. Wooden ones will eventually rot, but how long they'll last I don't know. They might well go on for years.
Crop bars are well worth the money in my opinion. I couldn't afford them when I bought mine and then had to bodge things when I added them about five years ago because the common tubing sizes appear to have changed, but I find them so useful now.
My tunnel doesn't have any ventilation unless the doors are open. Ideally I'd prefer it with hindsight, but it's not desperately bothered me in twenty years and is probably the sort of thing that a moderately competent bodger could add if necessary. I keep telling myself I'll do it when I next change the cover.
You definitely want at least one door (or set of doors) wide enough to get a wheelbarrow through, too.
Oh, buy some repair tape with the tunnel. At some point you're bound to need it (another reason for not using the anti-drip covers: repair tape doesn't stick to them very well).
James
