Great stuff, Joe - thanks for taking the time to put this together.
I'll add a few observations, and info on my recent trailer purchase - I ended up with a 5,000 LBS. GVWR Pacific Tandem
(Model G21TW4-5) for Da New Da Nag.
Tandem axles-tracks better, smooths out rough roads, MUCH SAFER DURING A BLOWOUT, greater weight reserve capacity, etc.
Add to that - smaller tires, which make the boat sit lower, and launch/retrieve easier. Personally, there's no way I'd tow with a single axle trailer, unless most of my trips were relatively local.
Roller bunks- much easier to launch, esp. at shallow ramps, or by yourself (generally), also is easier to pick up boat with sling for hoist launch, less maintainence (no carpet replacement), easier to clean hull with pressure washer, etc.
This one really boils down to choice, and how you choose to launch/retrieve your boat. Speaking as a bunk fan, here's why I like them.
If you like to power up onto your trailer, carpeted bunks are the way to go. With my truck tail-gate down, I can solo retrieve without getting my feet wet, even when there's no dock next to the ramp. Just drive the boat up until it sticks, step off the bow on the the trailer, crank the boat on, walk up to the tailgate which is out of the water, and step down.
Also, if you get the new super-slick linings on bunk trailers, they are almost as easy to launch and retrieve as rollers, particularly when wet. However, you lose the "stick" that's nice when powering up a carpeted bunk trailer. Bunk trailers usually sit lower than rollers; this may be an issue for storage (garage/shelter height), and in theory, makes for a better tow since the CG is lower - whether this is noticeable or not I don't know. And finally, the carpet maintenance on bunks is off-set by the lack of roller maintenance.
Good points. One more I'll add; all side guides are not created equal. I've seen some that were so flimsy, a slight bump while loading in a cross-wind was enough to bend or break them. If your manufacturer offers heavy-duty guides, get them. This is particualrly important if you drive your boat up onto the trailer. Also - make sure your guides are adjusted properly; I've found that a realtively tight fit works best - I'm guessing about a 3" clearance to the hull.
Get transom tie-downs that are rated for the job.
Along these lines - most trailers I've seen with the tie-down eyes have them welded or bolted in a fixed location on the trailer. Pacific sells one that wraps around the frame, so you can adjust the location. This can be nice if you have, or anticipate adding items to the top of your gunnels that may interfere with the straps (downriggers, etc.)
Would brakes on both axles be a worth-while improvement or over kill?
Check your local state regs - this may not be an option. I believe Les said WA requires brakes on both axles, while CA does not.
Here are a few more things to consider...
Welded vs. bolted - On the West coast, the only major manufacturer I'm aware of that sells a completely welded galvanized trailer big enough for a CD22 is
Pacific Trailers. Not being an engineer, I can't comment on any strength comparisons, but one advantage is better corrosion protection. There are no joints to move, which could eventually wear down the galvanized coating. It's also lighter for the same load capacity as others.
Stainless brake lines - Not sure if all manufacturers offer this, but at Pacific it was a relatively minor upgrade. Good insurance in my opinion.
Trailer width - This came as a surprise to me, but the width of common CD 22 trailers varies by as much as 10". This may not be a big deal to many folks, but if you have a tight storage area, it may come into play.
Fenders - This is a really minor nit pick, but I can't help but mention it. I really like the King Trailers sold up in WA - I would have gotten one from Les if it wasn't too wide for my storage needs. However - I hate the fact that the wheel fenders are individually molded around each of the tandem wheels. I constantly climb in/out of the boat on the trailer, and much prefer the way Pacific's fenders are made - one long, flat galvanized fender, that makes walking/stepping along the edge of the trailer much nicer. With the King, you have one step on top of each wheel.