When mounting some tubeless tires I've found it helpful to tie a rope/ cinch a strap around the centerline of the tire tread, then tighten it, as needed with a metal bar, as a windlass. This will help forced the bead against the rim, and help it seal quicker.
redk
Oh ! Almost forgot !
It's almost Always better to work with a warm tire.
Set it out in direct sun for 1/2 an hour or so before messing with it.
It makes a difference.
Yes, I use a wire wheel, wire brush, and/or sandpaper to assure the rim is clean and free of stuck debris beforehand, and have some soapy water applied to the tire bead with a rag.
.
