The key to ensuring you have a proper trailer for your boat, is to make sure:
1. The trailer"s net carry capacity is rated to carry the full wet weight of your boat. Make sure you have a clear understanding of your boat"s weight, for example, some boat manufacturers include the motor weight in the dry weight, and others do not. You need to account for fuel, water, waste, batteries, gear, life jackets, coolers, live wells etc. If you launching your boat with people on the boat, while it is on the trailer, be sure to account for them as well.
2. Make sure the support system on the trailer, whether it is with bunks or rollers, is set to properly support the hull, rather than cause hull or keel damage. Different companies have varying opinions on what is best for your boat"s hull. I firmly believe the best way to properly support you boat is to ensure there are properly fitted keel support bunks running down the center of the trailer. You want these bunks to be shaped like "V" to hug your keel. The bunks should be set according to your boat"s deadrise (angle of the keel). You will always want outer bunking as well, for stability that is shaped to curve your hull; bearing in mind they cannot hit a strake. This style bunking system also helps making loading and launching your boat very easy.
3. You want to make sure your boat"s entire transom is supported. The structure fiberglass/aluminum of your hull should not be hanging off the back of the trailer. This can cause undo stress to the hull. Also, each state has varying laws, but in most, the lights on the back of your trailer have to be within 3" of the furthest rear part of the trailer. For example: if you boat has a large transom bracket with two large outboard motors having off the back, more than likely you"ll need a frame extension to be road legal when towing.
4. You always want to properly tie your boat down to the powerboat trailer. Many people use the winch stand in the front as a tie down, and this is not accurate. You want to tie your boat down in the back, with either two tie downs from your transom eyes, to the back of your trailer, or with one long ratchet, up and over the rear of the boat. You also want to place a tie down from the bow eye on the boat, and strap it down to the trailer frame itself. The winch"s purpose is to help load your boat on the trailer, not to secure it to the trailer.
Just be sure, before purchasing a trailer for your powerboat that you make sure it will protect your hull, not damage it. Make sure it"s completely road legal and road worthy, so you can enjoy your boat, not have to stress about traveling!