Why dont you gang up a stack of 2pc 2x10s that's wide enough to bridge the truck, probably 8ft is enough.
Attach this to the bottom surface of the bottom truss chord using some basic 2x4 blocks, screwed. Now measure for 2pc 4x4 posts to go from the floor to the underside of the 2x10s, tap-fit on the length.
The trusses then just supply the side-forces so nothing tips over, which would be a serious problem in itself if it had to be independent like a gantry. The vertical loads are carried by the posts.
If you did split the load into 4 places it averages to ~250# corner. But then you need 4 lifting devices instead of one, and only 3 of the 4 are likely to be holding the load at any one time.