Dog, my trailer is a flatbed utility trailer. The bed is 5' wide by 8' long and I think the total length of the trailer is about 13 feet. The trailer axel, springs wheels and tires are rated for 3500 lbs. Even with the kayak bunks installed and three kayaks on board, I don't think I'm putting much of a strain on the trailer. My bunks are high enough that it puts the kayaks at windshield height. This ensures that the overhang of the boats will not drag when driveway ramps and such are encountered. It also puts the boats right up in the face of following vehicles.
Of course there is always the chance some careless driver could try to slam his windshield into my kayak, but that is also possible when longer kayaks are roof-topped.
When traveling at freeway speeds the boats are under very little stress, because my pickup bed cap breaks the wind. Consequently, I don't have to tie the boats down so tight. They ride on edge and are supported by upright braces--all are very well padded. As well as tying the boats down, I also have fore and aft restraining ropes. I'm not too concerned about losing a boat by accelerating too fast, but in the case of a panic stop, I wouldn't want to launch a kayak through the back window, or over the top of the truck.
I've never had a problem with parking at launch sites and in worst case scenarios, I detach the trailer and park it next to the truck. It only takes about a minute to do that. However, I do take the precaution of locking a big chain through one of the trailer's wheels. I wouldn't want to return from a nice paddle and find my trailer missing. That of course brings up a whole nuther subject--"safe parking at launch sites." I purposely avoid remote spots.