I ran into the same issue. Mine were separating near the light fixtures and at one point prevented the door from being opened. Our TT has over 25k miles over some rough roads, so it was not unexpected.
Like yours, my trusses above the ceiling trim are galvanized sheet metal. I debated whether to re- brad nail or to use screws. I ended up going to screws and did the modification last spring.
I painted stainless steel #6 Truss Head sheet metal screws (NOT the typical pan head at HD, to get a low head profile) using an etching primer and top coating with a white enamel.
In preparation for installing the painted screws, I marked and drilled holes the diameter of my awl in seven evenly spaced locations in a wood template the same width and length of the ceiling trim. I then used the template to mark all my ceiling trim. On ceiling trim where I could not use the full length template, I left them to be marked last. These were marked after cutting the template to a shorter length to avoid the obstruction, but still using the TT walls as a reference to ensure all the holes were along the same straight "sight lines".
I drilled a small pilot hole at each location before installing and removing a sacrificial unpainted
truss head screws. This way I was able to start the treads in the ceiling trim and sheet metal truss without damaging the painted screws.
After removing the sacrificial screw, I installed a painted screw while ensuring I was holding the ceiling trim tight against the truss.
I do not have a picture of the result, but I can say that you would have to study the ceiling to notice that the screws were used to support the trim.