You will need to get the empty trailer weight unless weight is already on title. Meaning, get the boat off the trailer, take trailer to a weigh station, and have the ticket register weight and VIN. They will not accept boat and trailer weight even with pictures, manufacturer weight stamps, etc. I fought it for weeks by going to different tax offices and still had to do this. Fee is based upon sales tax, registration sticker, and county.
Boat has to be registered at a TPWD location accepting registrations. Go to their site to see which is closest to you. Even now, due to covid, some locations are not accepting registration applicants. Forms are also on the site. Get a blank piece of paper and place over boat serial number, and use pencil to copy over to paper. Everything will be lined out on the site.