What is it you cannot find? There are forms and instructions online, though admittedly there are few instructions that address the specifics for a non-resident owner. Here is one that might help a bit. If you buy in Texas, the dealer will help with the title and registration process, but you may need some sort of Texas address for Texas legal documents.
http://ftp.txdmv.gov/pub/txdot-info/vtr/motor_vehicle_reg_manual.pdfYou will probably have to call a Texas DMV office to find out if your non-Texas address and non-Texas driving license ID can be used on the various application forms for a Texas vehicle title and registration (plate). Since they are adjacent to Mexico, they probably have some experience with this sort of thing. Make it clear the vehicle involved will be a camping trailer and not a motorized vehicle. The paperwork will be somewhat different.
A trailer does not require insurance because it is not a motor vehicle. Any insurance will be whatever you desire for your own protection, e.g. fire, theft, storm damage, etc. The tow vehicle will have liability insurance that covers any damage done by the trailer while underway.