I dicked around with this for about a month during the summer.
What eventually happened was I found some ~50lb struts with a 10" stroke, and mounted on the inside of the trailer. It worked fine I guess, but was not how I built the trailer originally.
I wanted ~20" stroke to allow use of the annex, and to clear my head to the bottom of the tent.
Your best option in my opinion, is to pony up for some actuators. They're cheap from China (I bought two sets of 4 for less than what a single one would cost me in Canada)
I think what has ultimately happened now, is that I'm just redoing the trailer to get close to the proper height from the start. The wife would like more storage in the trailer anyways...