@Karen Johnson yeah this is a real concern and you're right to flag it — the 1.5m spec is an open-sky figure, same as basically every GNSS module on the market, so dense canopy will absolutely affect it. How much depends on the constellation support and how the module handles weak/multipath signals, and the MultiNav Pro+ does run multi-constellation which helps a lot compared to single-constellation modules since you've got more satellite geometry to work with even when some signals are getting blocked or bounced around by trees.
That said, I wouldn't expect it to hold 1.5m under heavy canopy — realistically you're probably looking at something in the 3-6m range in moderate cover, and yeah it can get worse in genuinely thick old-growth type situations. The 18Hz fix rate actually works in your favor here though, because for trail logging you can post-process with some light filtering and the high sample rate gives you enough data points to smooth out the occasional bad fix rather than having it corrupt your whole track.
For a trail monitoring use case I'd honestly say it's still well-suited — the degradation you'll see is pretty typical across the category and the multi-constellation support puts it ahead of a lot of cheaper modules in these conditions. If you're hitting a stretch that's particularly brutal for signal, the track continuity from 18Hz will save you compared to a slower module that just gaps out entirely.
