TL;DR - I got a new, shorter antenna. And it's great. Should have done this a long time ago.
One of the biggest problems with a ham radio antenna installed on the roof of the truck is that low-hanging branches catch it, and try to pull the NMO mount out of the thin sheet metal. The biggest issue is the coil that exists in many antennas - to increase length and improve reception. To solve the problem, I replaced my Diamond NR770HBNMO mobile antenna (a great antenna that I still plan to run on trips where trees aren't an issue) with a STI-CO ROOF-FT-NITI mobile antenna. This antenna is about half the length, has no coil, and is so flexible that it can be tied in a knot.
I ran this antenna for the entire trip, and my APRS beacons were just as plentiful as they've been with the Diamond. My reception - regularly the best in my group - continued to exceed that of the other setups. So yes, this antenna seems great, and I'll be using it any time I'm headed into wooded areas!
I should note: this antenna is tuned by trimming it to length. I've trimmed it to a length that is optimized for approximately 145MHz, since I primarily tune my Ham radio within the 2m range - using 144.390MHz for APRS and 146.520MHz for simplex communications. This is part of the reason I may continue to run the Diamond antenna in situations where I can. Doing so will allow me to take full advantage of the 420-450MHz (70cm) range.
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