I installed the Roadmaster shock system and it definitely improved the ride for the 5th wheel. Although I did find that at least on the 2018 377's Jayco added a 2x3 piece of tubing under the I-Frame (welded) to mount the suspension. That eliminates the ability to install the upper shock brackets as shown in the installations to the I-Frame. I went to a spring shop and had them weld the upper shock mounts.
Not sure what problem you had on your 18 but mine is the same and I was able to install as per the directions, even with that boxed section. Shocks were proper length when level. The self tapping screws work on that tube. 7k miles later and holding properly.
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Todd
Just outside Philly
2018 377RLBH
2019 Ford F450 Platinum
Old Faithful: 2004 GMC Sierra 3500 Diesel Dually