There is a king of jack that can support very heavy loads A version of it is used to stablize houses in fact. This jack is either a tripod or square based pyramid shape with a screw down the center, Remove the screw and you can stack them. They also make one with a round "Bottle" type base. Like this one: SOUTHERN-TOOL.COM: Jet Screw Jacks
They come in assorted sizes (both height and weight capacity) and are very very reliable, Also, relative low cost.
make sure however, you have a proper "Support" point under the trailer.
NOTE: Found that company with a google search, Know nothing about them save part of what you see on that page (did not even read the whole page)