Thanks all for the comments. I've been looking at this on and off over the last week and have come to the conclusion that I'm better off spending my cash on a better tent in terms of quality and low weight to look after myself rather than the bike, which lets face it should be capable of being left out overnight even in the rain with no adverse effects. The tents with a garage are not only significantly heavier and more bulky, but are also expensive compared to better spec normal tents. There is always the possibility of carrying a lightweight cover for the bike that could also serve other duties if required.
It might be a few weeks away. I'll have no need for one until probably mid-June so will do my usual thing of keeping an eye on what's available at what price then pouncing when I see one worth having.
I would like one of these - the Terra Nova Starlite 2 Although, personally, 3 things I reckon to be against it Cost £445 for a tent to be used on spring / summer campsites only. Not going to be climbing Ben Nevis with it. Probably not great for hot weather, Europe in the summer can get very hot A bit - crawling around living on the floor on your hands and knees But otherwise a very capable, well made, lightweight and portable tent.