I think Sultan. I've talked to those guys before; they seem to be a quality shop.
However, Sam didn't indicate where he was on the price / performance scale.
If Sam's low on that scale, then I'd look into the want ads for a used boat trailer ... they're dirt cheap, often galvanized, usually as sturdy as a Paros for back roads, and easy to toss a piece of plywood on top to make a nice platform for a pontoon or raft.
You might look at the small raft trailer from Fishcraft (fishcraft.com). I've had mine for about three years now, and I'm very happy with it. The end roller and winch make it a breeze to load and unload. It is also very heavy duty & doubles as a small flatbed for hauling. I'm sure that you could get by with a lighter trailer, but it works just great with my 12 foot cataraft and plenty of gear. Fishcraft is in Sisters, Oregon.
You don't actually need a "raft trailer", unless you have the excess cash burning a hole in your pocket. All the years I whitewatered and have had fishing catarafts, I've never owned a true "raft trailer". But, I have had "redneck" raft trailers. I'd suggest modifying a boat trailer (easily found and cheap depending on what you want). I actually have modifying a couple driftboat trailers over the years. You don't need a full 12' long deck for a 12' boat. I only used a 4' x 8' deck for a 16' cataraft with no problems at all (can make a cover for the front if you're worried about stuff kicking up at the boat). You can buy a utility trailer for $199 at Sam's, Freddies, etc (when available that is, some of the newer ones at sams are running about $500 now). You'd get a true "utility" trailer that with just a simple modification, can be converted from a flat deck pontoon/raft trailer to a "haul around anything" trailer. Plus, they are ALOT cheaper then a raft trailer. The rear roller is nice, but not like you're loading/unloading a heavy aluminum driftboat. Dump the trailer in the water and lead the pontoon onto it and strap the front down. Then simply pull the boat out with your vehicle and finish the strap down process.
i have seen the $200 Utility Trailer w a slight addition of what looked like an 8 ft piece of 12 or 15 inch diameter pvc pipe that was cut in halves and fastended to the deck to cradle the pontoons, and they had putt what looked like a manual winch on the tongue of the trailer, It actually looked very utilitarian, andthey could not have had more than $250 into it and a little elbow grease
go for bigger wheels if you can, they last longer at high speeds. you can put some short sideboards on to get above the wheel wells and then add a deck for the pontoon. that leaves a nice storage compartment under the pontoon for oars, etc. no need to spend a lot. the trailers they now sell at lowes and HD as well as gi joes would also be easily converted. an old boat trailer is a good idea too. not like a pontoon weighs a lot.
Another cheap way to get by is to simply use channel strut (it's a metal tubing, shaped like a U) and bolt it down (they actually sell channel strut hangers that work awesome for trailers). Easy on and off applications with it. That way you can have your utility trailer, and in a matter of minutes have a pontoon/raft trailer. You really don't need a complete flatbed if you're hauling fully inflated. Never had a problem with my big boats on the strut, since you should have them inflated enough where they are taut. I got my strut from a fire system installer on a route I used to do. Not sure where you'd buy it in the general sector (maybe home depot????).