Wyo George Hi,
Pretty simple really. you will need all your documents. Passports,Drivers license, Car registration, Copy of title for boat , trailer, outboard receipt . Insurance ,US & Mexico.
When you cross the border you'll go into a special area to get a TIP Temporary Import Permit which is good for 5 years. Give them your paperwork, once their done walk over to the cashier and pay, then back to the original place and they stamp everything and your good to go. For my areas it's all right next to each other.
Make multiple sets / copies of all your US Doc's. This way when you go into any marina or are asked for them you already have a set to give them. It makes it faster and I feel it is a small curtesy to them.
So Far we have gone to Bay of Los Angeles and Puerto Escondido (Loreto) . PE is very nice with mast up storage for $200.00 per month and very safe. B of LA is great. You set up ,Launch and store your boat right in the same area. The is a nice family with a store and little casitas to rent where you can leave your rig.
Go and have fun. Drive slow and take your time