The orange dolly is a good idea when you know you'll have to get to the underside of a cannon. By the way, having enough space, including a 30' ceiling is very helpful. The train tracks through the garage are great whenever one of those 80 cm "Dora"-type pieces show up, you can just roll 'em in on a series of flatcars. And the little helper-guy, every cannon collector should have at least a dozen of 'em.
Of course none of this is mine, but now that I found this picture on the web I may have to construct at least one of those neato cannon dollies, I've been squeaking by with ordinary, unhandy, fragile piano boards for way too long.
CHANGE BY POSTER at 11:00 AM 1/22/12: There were some questions about possible copyright issues with the photo which I got from another forum, so that's easy to fix so there will be no questions. Here's a link to a webpage which has a different photo of the same tool and cannon, but this time has some explanation.
http://www.machuproject.eu/news/news-29.htm and here's the original photo which is in a PDF in the Dutch language, which may contain some other details on the cannon, simply copy text if possible and paste into "google translate" set for Dutch/English.
http://www.cultureelerfgoed.nl/sites/default/files/u4/Ouderogge.pdf