I don't think the factory started installing struts until 2019 model year. The struts the factory put on my early 2019 T21TBHW (A213HW) were mismatched in length and rated at 40lbs. The strut model number (stamped on the strut) gives open length and power rating. They were nowhere near enough power, which was surprising because the dormer struts are well matched to the load.
I installed 60# struts, but it's not quite enough - probably needs 80# with the combination of dormer weight and poor location of the struts, but the roof isn't strong enough to handle that much force that near the hinge. The design really needs to lift near midpoint or further back for decent leverage. The angle appears about right (almost 90 degrees when the roof is up), just too close to the hinge.
I finally tested taking the lift motor off this week on a camping trip. I was able to raise the roof manually by pushing up on the rear handle with a wood pole. But the roof did not raise as evenly as I would have liked - it does better with the lift motor. And I had to push about 40lbs force, which I was afraid was going to rip the handle off the aluminum cap. There was definitely an assist from the struts, but not enough for a smooth experience. Compared to OYO's experience, I think the dormer weight is the issue. I can't use more power in the struts because they are already causing warping of the aluminum at the upper mount.
In an ideal world, I would retry the experiment, moving the struts back as far as I could without interfering with door or hatches (or grills for heater, water, heater, and fridge on the port side). This would take considerably longer struts. But I am not going to make new holes in the side of my A-frame or roof frame. So I will live with the electric lift with a good assist from the 60# struts where they are. Since Forest River gave me a second lift motor under warranty, I'm going to take the first lift motor apart, clean and lube the gears, and see if I can put a better seal where the shaft goes into the case.
just my thoughts and experiences
2019 Flagstaff T21TBHW A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time
last trip: Trinidad, CO (earlier this week)
next trip: Black Hills (2 June)