Is this inside the wheel wells or outside?
If inside the wheel wells I would use Sikaflex 221 which is available in black, gray and white. I have used this caulk and is easy enough to work with.
If outside you could probably still use the sikaflex but I would use some blue painters tape, small caulking tip and a steady hand.
Use a nitrile glove and strike the caulk joint with mineral spirits.
Steve, Christy, Anna and Phoebe (Border Collie)
1994 Classic 30'11" Excella - rear twin
2009 Dodge 2500, 6 Speed Auto, CTD, Quad Cab, Short Bed
Hensley Arrow hitch with adjustable stinger
WBCCI # 3072