Here's a thought:
If you have specific tools and other items that pertain only to towing your trailer and don't have a convenient place in your tow vehicle for them (especially a problem with some of the more compact vehicles we often use these days), why not set up a dedicated tool box on your boat trailer for them?
There's usually a space below and behind the bow strut that is open and unused that could be fitted with a box for carrying that special jack, wrench, safety jack stands, wooden blocks, a grease gun, extra bearings, light bulbs, extra ropes, bungees, etc. Mount the box athwartships (side to side) so it won't block your walking outward on the trailer tongue during launching and retrieval, etc.
Such a box would have to be waterproofed, locked, and probably constructed of metal for security, etc.
It could be bolted to the trailer frame with U-bolts down through the bottom of the box, then sealed with silicone or something else suitable.
Get an aluminum diamond plate box, or simply paint a plain metal one to match the color trailer or the boat. (Two- tone top and bottom to match your C-Dory color scheme?)
I could see it being a liability for those who have to leave their trailers in unsecured lots for extended periods when going on long cruises, but if it were designed instead with the U-bolt threads facing upward and terminated in the box with rubber washers for sealing, it could be removed quickly and hidden in the now relatively empty tow vehicle under a nondescript cover, such as an old blanket or blue plastic tarp.
(I once built a trailer for carrying two small El Toro sailboats and used a surplus heavy metal Army footlocker for a storage box. With a Abus stainless steel lock and hasp, it was pretty secure without at least a three foot crowbar.)
Just another fun project to consider, if you can figure out how to make it work for you!
Joe. :teeth :thup