On Monday, December 9, 2013 7:52:49 PM UTC-5, Bob Kuykendall wrote:
To estimate the force required to hold the trailer top open,
the easiest way is to just use bathroom scales or similar
to see how much force is required when the trailer is fully
open.

Right - Prop the trailer open using a 2x4 cut to length,
propped at the spring attach, angled in the direction of
the spring, against a scale held in the proper orientation.
You'll need a helper to prevent dropping the trailer
top when you do this and a 2nd 2x4 for the opposite side...

We're waiting for the video.
DON'T DROP THE TRAILER TOP !

Have fun, See ya, Dave