I haven't built or trailered a NE Dory, but have searched for trailers for other light craft.  One option is to build your own (search the web for plans).  Another is to find a used jet ski trailer, especially one that carried only a single jet ski.  Your biggest concerns should be about tires, bearings, and lights.  You can modify the length of the trailer (welding skills needed) and adjust the springs (remove leaves) to better adapt to the dory's length and weight.  And decrease the tire's air pressures so the trailer doesn't bounce too much.  You'll need enough air pressure so the tires don't come off their wheels, with only enough air so that the side walls flex just slightly when the trailer is loaded.  Depending on the tires you use (most of them will be rated to each carry much more weight than you'll have - dory + trailer + stuff), you might  want to err with too much air (25 psi?).  Check the temperature of the tires after driving at speed for a while.  They should be almost cool to the touch.  If they are hot, add air.  Take a 12V air pump or a bicycle pump (check it works with your tires' valve stems) with you in case you need to add air.  Good luck.

Harbor Freight makes some trailers you can order on line.  I just googled their site and found they also make a small boat trailer.  Seems their trailers are around the 300-400 range and may serve your purposes.  Now that I'm looking I'm thinking a flat bed trailer may have been useful to me for my Skerry as it could be used for multiple things/boats/toys.

A trailer such as the #5002 on the above mentioned site will be OK. For freeway speeds remember that 8" wheels will rotate at over twice the RPM of your car tires so keep the hubs well greased. SEEYA Jack

I just purchased a HF trailer and 20' of 2x3 steel tubing. I have to drill 3 holes in the tubing to match the trailers hole patterns. 3 - 1/2" bolts secure the 2x3 steel tubing to the frame, replacing the factory supplied tongue. my neighbor had an extra coupler for a 2" tongue. I bought a book on trailers, but this link was enough to get me started. 

http://www.ehow.com/how_6064525_build-own-jon-boat-trailer.html

I'm installing a keel roller and a bowstop with a winch just for good measure.

Thanks, Tim

http://thenortheasterdoryproject.wordpress.com/

Would the 5002 model need to be modified?  I ask since the website says it is meant for boats 12 to 14 feet in length...The dory is 17.  

I used a small utility trailer as a base.(90153). I had considerd the 5002 model but thought that I could modify the one that I got better and it fit the description of the Jon Boat trailer....and I wanted 12" wheels and tires.

All I have to do is bolt the 2"x3"x16' backbone to the frame. add a tongue extender, a bow stop, a keel roller and some bunks and a jack and coupler and I'm done. Well I'm not done, but it is straight forward.

Hope this helps.

Tim

http://www.harborfreight.com/automotive-motorcycle/trailer-accessories/1090-lb-capacity-40-1-2-half-inch-x-48-inch-mini-utility-trailer-with-12-inch-four-lug-wheels-and-tires-90153.html

I found a used Karavan trailer (model 1250-46) for my dory.  This may be the smallest trailer the company makes but it works well.  The trailer and the 12" wheels are made of galvanized steel, and the whole thing (trailer and boat) is still light enough for me to pick up and move by myself.

Timotaeus, please elaborate on 'the 2"x3"x16' backbone'. Is that square metal tubing, a wood glue-up or what?

Ok, I think I understand that the backbone is a square steel tube mounted on the center of the trailer with rollers mounted to support the bottom of the Dory. I will see what ETrailer has along those lines.

I found this link: http://forum.woodenboat.com/showthread.php?65723-Dory-Trailer that shows the Harbor Freight trailer with a replacement rectangular steel tube (2.5"x2" ?).l

Like this...

I just bought the HF boat trailer and have made two changes that should help.

I removed the bottom spring leafs to soften the suspension and replaced the 8 inch wheels with 12 inchers. The bolt pattern is 4X4". It will be a simple matter to raise the fenders for clearence.

FWIW the load rating of 4.80 X 8 and 4.80 X 12 tires at 30 psi is 380 and 545 pounds respectively.  

HF sells two versions of the trailer, one with 8" wheels(Item #42708) and the other 12" wheels(Item #90153), about $40 difference.

Thanks, bshaw & autonomous, for the vector to Harbor Freight for a NE Dory trailer. Here is Haulmaster #90154 with runners and wooden cradle boards. The trailer tongue is 10 feet of 2 1/8 square 3/16th steel.

No wiring, winch just bolted on, and no bow anchor bolt yet (I dread having to drill a straight hole through 1X6 oak bowstem).

Denny