Also break down the price for each, $$ for boat, $$ for motor, and $$ for trailer on the bill of sale. this is because you get the trailer registered at the county license dmv and the boat motor at tpwd for taxes. they both want their share out of you. also fill out tx form 130u for trailer registration. the seller has to sign this. at least i had to file this form in tarrant county. good luck.
Actually, when buying mine it was bill of sale'd for the whole package. I registered boat first, and they had me carry my receipt documentation with me to get the trailer registered showing I had already paid the TPWD the sales tax as a whole. No problems. But do have full identification details for boat, motor, trailer on bill of sale. Breakdown of the costs didn't turn out to be necessary in my experience.
I think a lot of of it depends on the person behind the counter at both places. The more paperwork you take in, the easier it'll be for your get titles and registered.
You don't have to title a trailer unless it's been titled before. If it has, a title for trailer is required as well as boat and motor titles. All I know for sure is that it's a PIA to go through all of it. GL!
I think the title depends on trailer size, but I'm not totally sure. My current boat trailer was titled by the previous owner and when I registered it, she told me no title is required. IDK. If I ever have an issue I have the previous owner title signed over to me. Everyone s experience I talk to is different. TX is just jacked up when it comes to this stuff.
Good Luck.