I have a few adjustable rod holders suitable for rail or side mounting. These came from a shop that used them only for display of rods or rod & reel combos so they are technically second hand but have never been used in the field.
This professional rod holder is designed for light trolling. It easily fits to a boat by a rail, and can be adjusted to give just the right angle to fish your lure properly.
Made of Corrosion Proof Polypropylene
Has Rotating Locking Ring
Fully Adjustable Horizontally & Vertically
Rail or Side Mounted
Comes with 4 Stainless Mounting Screws & Nuts